RADIATION PROTECTION IN DENTISTRY AND ORAL AND MAXILLOFACIAL IMAGING

Transcription

1 NCRP DRAFT SC 4-5 REPORT RADIATION PROTECTION IN DENTISTRY AND ORAL AND MAXILLOFACIAL IMAGING Note: Copyright permission is being sought for the figures and tables requiring such permission prior to their use in the final NCRP publication. National Council on Radiation Protection and Measurements 7910 Woodmont Avenue, Suite 400, Bethesda, Maryland 20814

2 1 Preface No exposure to x rays can be considered completely free of risk, so the use of radiation by dentists and their assistants implies a responsibility to ensure appropriate protection. The Report provides radiation protection guidance for the use of x rays in dental practice including the use of intraoral imaging, cone beam computed tomography, digital imaging radiation protection devices, and hand held x-ray systems The aim of the Report is to provide a practical radiation protection guide for dentists and their assistants. Information is presented in a clear and comprehensive format focusing on dental radiological practices This Report is dedicated to the memory of S. Julian Gibbs, DDS, PhD, former Professor of Radiology and Radiological Sciences at Vanderbilt University. Dr. Gibbs was the Co-Chair of Scientific Committee 91, that was responsible for NCRP Report No. 145, Radiation Protection in Dentistry, and he served as a member of the Council for many years. His research interests focused on radiation doses from medical and dental radiologic procedures, and he was a pioneer in applying computational techniques to studies of radiation dose distribution to critical organs. He was a true scholar and humanitarian, and was an inspiration and beloved mentor to dentists who pursued careers in the radiation sciences This Report supersedes NCRP Report No. 145, Radiation Protection in Dentistry, which was issued in December This Report was prepared by Scientific Committee 4-5 on Radiation Protection in Dentistry. Serving on Scientific Committee 4-5 were: Co-Chairs 27 Alan G. Lurie University of Connecticut School of Dental Medicine Farmington, Connecticut Mel L. Kantor University of Wisconsin-Eau Claire Institute for Health Sciences Eau Claire, Wisconsin 2

3 28 Members 29 Mansur Ahmad University of Minnesota School of Dentistry Minneapolis, MN John B. Ludlow University of North Carolina, School of Dentistry Chapel Hill, North Carolina Eleonore D. Paunovich Veterans Health Administration San Antonio Texas Robert A. Sauer Food and Drug Administration Center for Devices and Radiological Health Silver Spring, Maryland Veeratrishul Allareddy University of Iowa College of Dentistry Iowa City, Iowa Edwin T. Parks Indiana University School of Dentistry Indianapolis, Indiana Robert J. Pizzutiello Landauer Medical Physics Victor, New York David C. Spelic Food and Drug Administration Center for Devices and Radiological Health Silver Spring, Maryland Consultants 33 Edwin M. Leidholdt, Jr. Veterans Health Administration Mare Island, California Donald L. Miller Food and Drug Administration Center for Devices and Radiological Health Silver Spring, Maryland William Doss McDavid University of Texas Health Science Center at San Antonio San Antonia, Texas Madan Rehani Harvard Medical School and Massachusetts General Hospital Boston, Massachusetts

4 36 NCRP Secretariat Joel E. Gray, Staff Consultant Cindy L. O Brien, Managing Editor Laura J. Atwell, Office Manager James R. Cassata, Executive Director, 2014 David E. Smith, Executive Director, The Council wishes to express its appreciation to the Committee members for the time and effort devoted to the preparation of this Report, and to the following organizations for providing financial support during its preparation: American Academy of Oral and Maxillofacial Radiology American Association of Physicists in Medicine American Board of Radiology Foundation American Dental Education Association Food and Drug Administration, Center for Devices and Radiological Health John D. Boice, Jr. President 56 4

5 57 Contents Executive Summary General Purpose of the Report The Most Significant Methods to Minimize Radiation Dose, and Maximize Image Quality and Diagnostic Efficacy Quality Assurance of Radiology in the Dental Office Education and Training Introduction Purpose Scope Radiation Protection Philosophy General Considerations Dose Limits Role of Dental Personnel in Radiation Protection The Dentist Auxiliary Personnel The Qualified Expert Electronic Image Data Management Radiation Protection in Dental Facilities General Considerations Shielding Design Equipment Performance Evaluations and Radiation Protection Surveys Signage Diagnostic Reference Levels and Achievable Doses Optimization of Image Quality and Patient Dose. General Principles Protection of the Patient Selection Criteria Examination Type and Frequency Symptomatic Patients Asymptomatic Patients

6 Administrative Radiographs X-Ray Machines Examinations and Procedures Intraoral Radiography Panoramic Radiography Cephalometric Radiography Fluoroscopy Cone Beam Computed Tomography Image Viewing Environment Viewing Conditions for Digital Images Use of Radiation Protective Aprons Use of Thyroid Collars Maintenance of Protective Aprons and Thyroid Shields Special Considerations for Pediatric Imaging Protection of the Operator Shielding Design Barriers Distance Position of Operator Personal Dosimeters Protection of the Public Quality Assurance and Quality Control Image Quality and Patient Dose Optimization Image Quality Patient Dose Technique Charts Quality Control Radiation Measurements of X-Ray Producing Dental Diagnostic Equipment Phantoms for Quality Control and Dose Measurements Quality Control for Film Imaging Quality Control for Digital Image Receptors Quality Control for CBCT Quality Control for Image Displays

7 Quality Control Tests and Frequency for Digital Radiography Infection Control Image Receptors Direct Exposure X-ray Film General Information Equipment and Facilities Darkroom Fog Storage of Radiographic Film Film Processors Screen-Film Systems General Information Equipment and Facilities Care of Screen-Film Systems for Film-Based Cephalometric and Film-Based Panoramic Imaging Screen-Film Speed Recommendation Digital Imaging Systems General Information Proportion of Digital versus Film, Proportion of PSP versus CMOS-CCD Advantages of Digital Imaging Compared to Film Imaging Potential for Dose Reductions for PSP and DR Compared with Film Disadvantages and Challenges of Digital Imaging Equipment and Facilities PSP Plates Solid State Receptors Converting from Film to Digital Imaging Potential Dose Reduction Technique Charts Clinical Image Display Monitors for Digital Imaging Intraoral Dental Imaging General Considerations Beam Energy Position-Indicating Devices Rectangular Collimation

8 Patient Restraint Diagnostic Reference Levels and Achievable Doses Best Practices FDA Clearance of Dental Imaging Equipment Conventional X-Ray Systems(Wall Mounted and Portable) General Information Equipment and Facilities Protection of the Operator and Shielding Tube Head Positional Stability Positioning-Indicating Devices Rectangular Collimation Hand-Held X-Ray Systems General Information Advantages of Hand-Held X-Ray Units Disadvantages of Hand-Held X-Ray Units Safety Issues with Improper Handling of Hand-Held X-Ray Equipment Exception to Never Hold the X-Ray Tube Equipment Backscatter Shield Leakage Radiation Radiation Protective Equipment and Personal Radiation Monitoring Appropriate Use of Hand-Held X-Ray Machines in Dental Offices Comparison to European Recommendations Position-Indicating Devices Rectangular Collimation Extraoral Dental Imaging Panoramic General Information Diagnostic Reference Levels and Achievable Doses Bitewings from Digital Panoramic Machines Equipment and Facilities Cephalometric General Information

9 Diagnostic Reference Levels and Achievable Doses Equipment and Facilities Cone-Beam Computed Tomography General Information Dose Comparisons for CBCT and MDCT Machines Use of Simulated Bitewing. Panoramic and Cephalometric Views from CBCT Data Number of CBCTs in the United States and Growth Rate Efforts Regarding CBCT in Europe SEDENTEXCT and Evidence-Based Guidelines Patient Selection Criteria for CBCT Implants Oral and Maxillofacial Surgery Periodontal Indications Endodontic Indications Temporomandibular Joint Indications Caries Diagnosis Indications Sinonasal Evaluation Indications Craniofacial Disorders Indications Orthodontics Obstructive Sleep Apnea Equipment and Facilities Radiation Dose Structured Report Equivalent Needed for CBCT Advantages of Pulsed Systems over Continuous Radiation Exposure Systems Advantages of 180 Degree Scan versus 360 Degree Scans Location of Equipment and Requirements for Shielding Administrative and Education Administrative and Regulatory Considerations Compliance with FDA Medical Device Regulations and Electronic Product Radiation Control Performance Standards General Considerations Hand-Held X-ray Devices

10 CBCT Units Advanced Diagnostic Imaging Accreditation Education and Training Digital Imaging Hand-held Imaging Systems Practitioner Additional Safety Concerns Operator Training Qualified Expert Required Information CBCT Imaging Systems Training for Practitioners Training for Operators Training for Qualified Experts Continuing Education for Practitioners, Operators, and Qualified Experts Summary and Conclusions Appendix A. Quality Control for Film Processing A.1 Five Basic Rules for Film Processing A.2 Quality Control A.2.1 Sensitometry and Densitometry A.2.2 Dental Radiographic Quality Control A Dental Radiographic Quality Control Device A Aluminum Step Wedge A Lead Foil Step Wedge A Reference Film Appendix B. Quality Control for Digital Imaging Systems B.1 Quality Control of Digital Intraoral Systems B.1.1 The Display B.1.2 Quality Control Phantoms B.1.3 Baseline Exposure Assessment B.1.4 Baseline Image B.1.5 Follow-up Images B.1.6 Record Keeping

11 Appendix C. Historical Aspects of Digital Imaging Appendix D. Shielding Design for Dental Facilities D.1 General Shielding Principles D.2 Shielding for Primary and Secondary Radiation D.3 Shielding Principles D.4 Occupancy Factors, Use Factors, and Workloads D.4.1 Occupancy Factors D.4.2 Use Factors D.4.3 Workloads D.5 Summary Appendix E. Dosimetry, Intraoral, and Panoramic Imaging E.1 Patient Dosimetry E.2 Operator Dosimety Appendix F. Dosimetry for Multidetector-Multislice Imaging of Dentomaxillofacial Areas Appendix G. Dosimetry for Dental Cone Beam CT Imaging Appendix H. Dental X-Ray Evaluation by Qualified Expert H.1 Radiation Safety H.2 Evaluation of the Image Receptor and Dose H.3 Film Processing Conditions and Quality H.4 Evalutation of the X-Ray Generator and Output H.5 Evaluation of the Beam Collimation H.6 Occupational Radiation Exposure Assessment Appendix I. Radiation Risk Assessment I.1 Introduction I.2 Definitions I.2.1 Stochastic Effects

12 I.2.2 Deterministic Effects (Tissue Reactions) I.2.3 Dose Language I.3 Studies of Irradiated Human Populations I.3.1 Introductions I.3.2 Atomic Bomb Survivor Lifetime Studies I.3.3 Children Irradiated for Tinea Capitis and Enlarged Thymus I.3.4 Females Receiving Fluoroscopy for Tuberculosis Treatment Follow-up I.3.5 United Kingdom National Registry of Radiation Workers I Australian CT Study of Electronic Medicare Data I.4 Effects of In Utero Exposure I.5 Effects on Children I.5.1 Joint Commission Report (2011) I U.K. Study of Head CT Scans in Children I.6 Heritable Genetic Effects I.7 Risk from Traditional Oral and Maxillofacial Imaging: Intraoral, Panoramic, and Cephalometric I.8 Risk from CBCT Imaging I.9 Other Risks in Daily Living for Comparison Appendix J. Radiation Quantities and Units Abbreviations, Acronyms and Symbols Glossary References

13 Executive Summary General Radiology in dentistry is omnipresent, as evidenced by the approximately one billion intraoral images produced in the United States in 2014 to 2015 (Farris and Spelic, 2015). In the 15 y since the prior NCRP report, NCRP Report No. 145, Radiation Safety in Dentistry, three innovations have found significant application throughout general and specialty dentistry: digital acquisition of images, hand-held intraoral imaging devices, and cone-beam computed tomography (CBCT) Dentistry is unique in that most dentists in private practice are not only the treating clinician but also both the radiologist and radiation safety officer in the office. Use of x-ray imaging in dental practice, in particular digital imaging and CBCT, has increased steadily for decades and we anticipate this trend to continue. Conversely, the average radiation exposure for individual intraoral, panoramic and cephalometric images have decreased. However, the addition of CBCT to dentistry, with the potential for use of inappropriate exposure parameters or inappropriate use, along with persistence of round collimation and D-speed film for intraoral imaging, require concerted, focused efforts towards optimization to achieve and maintain diagnostic quality imaging at the lowest possible radiation dose [as low as reasonably achievable (ALARA) principle] Purpose of the Report The purpose of this report is to enhance radiation safety in dentistry and to reinforce published, well-known dose-reduction methods that are not yet being widely applied in the dayto-day practice of dentistry. The technological advances since NCRP Report No. 145 (NCRP, 2003) require changing attitudes and practices of dentists because opportunities are now present for decreasing radiation doses while improving diagnostic efficacy. This report updates the material in NCRP Report No.145, adds new content on digital imaging, hand-held x-ray devices, 13

14 CBCT, and makes recommendations for reducing patient radiation doses and improving image quality, all in the context of the ALARA principle The Most Significant Methods to Minimize Radiation Dose, and Maximize Image Quality and Diagnostic Efficacy Many of the recommendations in this report are grounded in the recommendations of NCRP Report No. 145, and are recommendations that could be quickly and inexpensively employed in today s dental practice environment. They include: Use selection criteria for every imaging examination. Use the fastest imaging receptor possible for all intraoral and extraoral imaging. For intraoral imaging use either ANSI F-speed film or digital receptors. Eliminate D-speed film. Use rectangular collimation for all intraoral imaging except where patient anatomy or behavior does not allow its use. Use thyroid collars for all intraoral imaging and extraoral imaging (panoramic and cephalometric) where it does not interfere with the required diagnostic information on the image. Ensure technique factors or imaging protocols are optimized to produce adequate images with the lowest dose to the patient. Follow the film manufacturers guidelines for processing film Additionally, new recommendations pertaining to acquisition technical factors and indications for use are provided for digital, hand-held, and CBCT imaging: Employ appropriate selection criteria for obtaining CBCT images. Acquire CBCT images using the smallest field of view and acquisition technical factors that deliver the needed diagnostic information at the lowest possible radiation dose. Use only x-ray units which have been cleared by the U.S. Food and Drug Administration (FDA). This is especially true with hand-held, intraoral x-ray devices. 14

15 Embrace the efforts of Image Gently be mindful of the greater sensitivity to radiation damage in children, conduct imaging exams only when clinically warranted, and downsize radiation doses accordingly, with consideration of the diagnostic requirements of the imaging task Quality Assurance of Radiology in the Dental Office The dentist, with the assistance of the qualified expert, must establish and implement protocols and procedures for the safe and effective use of diagnostic radiology in the office. This includes maintenance and optimization of dental imaging equipment and quality control of the components of digital imaging systems Education and Training Advances in imaging technology, especially with the rapidly increasing use of CBCT imaging, require more education and training of dentists and staff in the safe and effective use of such technologies. Such training is not within the expertise of salespersons and must be conducted by trained professionals from the manufacturers and by qualified experts The following Table 1.2 lists all of the recommendations made in this report in the order in which they appear in the subsequent chapters. The subsection in which each statement appears and is discussed is noted in the right-hand column. The recommendations should not be read in isolation. The reader should consult the indicated subsection for more complete explanations and further information Two terms used in this Report have a special meaning as indicated by the use of italics Shall and shall not are used to indicate that adherence to the recommendation is considered necessary to meet accepted standards of protection. 2. Should and should not are used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances. 15

16 414 TABLE 1.2 Recommendations. Number Recommendation Section 1 No individual worker shall receive an occupational effective dose in excess of 50 msv in any 1 y. 2 The numerical value of the individual worker s life-time occupational effective dose shall be limited to 10 msv times the value of his or her age in years. Occupational equivalent doses shall not exceed 0.5 msv in a month to the embryo or fetus for pregnant individuals, once pregnancy is known. 3 Mean nonoccupational effective dose to frequently or continuously exposed members of the public shall not exceed 1 msv y -1 (excluding doses from natural background and medical care); infrequently exposed members of the public shall not be exposed to effective doses >5 msv in any year. 4 The dentist (or, in some facilities, the designated radiation safety officer) shall establish and periodically review a radiation protection program. The dentist shall seek guidance of a qualified expert in this activity. 5 The dentist shall employ published. evidence-based selection criteria when prescribing radiographs. 6 Radiological procedures shall be performed only by dentists or by legally qualified and credentialed auxiliary personnel. 7 The qualified expert should provide guidance for the dentist or facility designer in the layout and shielding design of new or renovated dental facilities and when equipment is installed that will significantly increase the air kerma incident on walls, floors, and ceilings. 8 The qualified expert shall provide guidance for the dentist regarding establishment of radiation protection policies and procedures

17 9 To avoid unnecessary repeat exposures due to lost images or redundant examinations, the electronic image data management system shall provide for secure storage, retrieval, and transmission of images All digital images acquired shall be retained in the patient s electronic record All digital images should be backed up offsite electronically in a separate, safe, and secure location at regular intervals. 12 The qualified expert should perform a pre-installation radiation shielding design and plan review, to determine the proper location and composition of barriers used to ensure radiation protection in new or renovated facilities, and when equipment is installed that will significantly increase the air kerma incident on walls, floors, and ceilings. 13 The qualified expert shall perform a post-installation radiation protection survey to assure that radiation exposure levels in nearby public and controlled areas are ALARA and below the limits established by the state or other local agency with jurisdiction. 14 The qualified expert should assess each facility individually and document the recommended shielding design in a written report. 15 The qualified expert should consider the cumulative radiation exposures resulting from representative workloads in each modality when designing radiation shielding for rooms in which there are multiple x-ray machines. 16 The facility shall establish administrative controls that assure no more than one patient is in an x-ray room with multiple x-ray machines during any x-ray exposure. 17 A qualified expert shall evaluate x-ray equipment to ensure that it is in compliance with applicable governing laws and regulations. 18 All new dental x-ray installations shall have a radiation protection survey and equipment performance evaluation carried out by, or under the direction of, a qualified expert

18 19 Equipment performance evaluations shall be performed by a qualified expert at regular intervals thereafter, preferably at intervals not to exceed 4 y for facilities only with intraoral, panoramic or cephalometric units. Facilities with CBCT units shall be evaluated every 1 to 2 y. 20 Diagnostic Reference Levels and Achievable Doses should be developed for dental CBCT imaging. 21 Each dental facility should record and track indicators of patient dose, such as entrance air kerma and associated technique factors. 22 Each dental facility should compare its doses to DRLs and ADs. In particular, where established methods exist, the qualified expert shall collect dose data suitable for comparison with DRLs and ADs. These data and the results shall be provided in the qualified experts report. For dental imaging systems that provide dose metrics for patient examinations, the dentist or qualified expert should periodically compare medians of these data for 10 clinical examinations appropriate for this purpose with DRLs and ADs. 23 Organizations such as NCRP, U.S. Food and Drug Administration (FDA), Conference of Radiation Control Program Directors (CRCPD), American Academy of Oral and Maxillofacial Radiology (AAOMR), and American Dental Association (ADA) should strive to provide DRLs and ADs for a variety of dental examinations. 24 All radiological examinations shall be performed only on direct prescription of the dentist, physician, or other individuals authorized by law or regulation. 25 Radiographic examinations shall be performed only when patient history and physical examination, prior images, or laboratory findings indicate a reasonable expectation of a health benefit to the patient. 26 For each new or referred patient, the dentist shall make a good faith attempt to obtain previous, pertinent images prior to acquiring new patient images

19 27 For symptomatic patients, the radiological examinations shall be limited to those images required for diagnosis and treatment of current disease. 28 For asymptomatic patients, the extent of radiological examination of new patients, and the frequency and extent for established patients, shall adhere to current published, evidence based selection criteria. 29 Administrative use of radiation to provide information that is not necessary for the treatment or diagnosis of the patient shall not be permitted. 30 Students shall not be compelled or permitted to perform radiographic exposures of humans solely for purposes of education. 31 Candidates shall not be compelled or permitted to perform radiographic exposures of humans solely for purposes of licensure, credentialing or other certification. 32 Personnel responsible for purchase and operation of dental x-ray equipment shall ensure that such equipment meets or exceeds all applicable U.S. federal government and state requirements and regulations. In addition, the equipment should conform to current international standards for basic safety and essential performance. 33 Fluoroscopy shall not be used for static imaging in dental radiography. If fluoroscopy is used for dynamic imaging, the practices in NCRP Report No. 168 shall be followed. 34 Images shall be viewed in an environment adequate to ensure accurate interpretation. 35 The use of radiation protective aprons on patients shall not be required if all other recommendations in this Report are rigorously followed unless required by state regulation. Otherwise, a radiation protective apron shall be used. 36 Thyroid shielding shall be provided for patients when it will not interfere with the examination

20 37 Protective aprons and thyroid shields should be hung or laid flat and never folded, and manufacturer s instructions should be followed. All protective shields should be evaluated for damage (e.g., tears, folds, and cracks) quarterly using visual and manual inspection. 38 Technique factors and selection criteria shall be appropriate to the age and size of the patient. 39 Adequacy of facility shielding shall be determined by the qualified expert whenever the average workload increases by a factor of two or more from the initial design criteria. 40 Shielding designs for new offices with fixed x-ray equipment installations shall provide protective barriers for the operator. The barriers shall be constructed so operators can maintain visual contact and audible communication with patients throughout the procedures. 41 The exposure switch should be mounted behind the protective barrier such that the operator must remain behind the barrier during the exposure. 42 In the absence of a barrier in an existing facility, the operator shall remain at least 2 m, but preferably 3 m, from the x-ray tube head during exposure. If the 2 m distance cannot be maintained, then a barrier shall be provided. This recommendation does not apply to hand-held units with integral shields. 43 Provision of personal dosimeters for external exposure measurement should be considered for workers who are likely to receive an annual effective dose in excess of 1 msv. Personal dosimeters shall be provided for declared pregnant occupationally-exposed personnel. 44 For new or relocated equipment, the facilities shall provide personal dosimeters for at least 1 y in order to determine and document the doses to personnel. 45 The facility shall provide personal dosimeters for all new operators of handheld dental x-ray equipment for the first year of use

21 46 In dental facilities using large, multi-patient open bay designs, a patient in proximity to another patient being radiographed shall be treated as a member of the public for radiation protection purposes. 47 When portable or hand-held x-ray machines are used, all individuals in the area other than the patient and operator shall be protected as members of the public. 48 New dental facilities shall be designed such that no individual member of the public will receive an effective dose in excess of 1 msv annually. 49 X-ray machines should provide a range of exposure times suitable for twice the speed of the fastest available image receptors. 50 A suitable radiographic phantom shall be used to optimize radiation dose and image quality, and for continuing quality control measurements. 51 Film processing quality shall be evaluated daily, before processing patient films, for each film processor or manual processing system. 52 There shall be an infection control policy to protect staff and patients that encompasses imaging equipment and procedures. 53 Imaging equipment and devices should be designed to facilitate standard infection control precautions. 54 Image receptors of speeds slower than ANSI Speed Group E-F film shall not be used for intraoral radiography, i.e., D-speed film shall not be used. 55 Each darkroom and daylight loader shall be evaluated for fog at initial installation, and then at least quarterly and following change of room lighting or darkroom safelight lamp or filter. 56 Film, including film in cassettes, shall not be exposed to excessive radiation during the period it is in storage

22 57 Film shall be processed with active, properly replenished chemicals and timetemperature control, according to manufacturers recommendations. 58 Screen-film systems of speeds slower than ANSI 400 shall not be used for panoramic or cephalometric imaging. Rare-earth systems shall be used. 59 The dental practice should enlist the assistance from a qualified expert to ensure each new digital system is properly configured with regard to both patient dose and image quality. 60 When converting from film to digital imaging, the facility shall make proper exposure technique (time) adjustments, commensurate with the digital imaging system. 61 The operating potentials of intraoral dental x-ray units shall not be <60 kvp and should not be >80 kvp. 62 Position-indicating devices shall be open-ended devices and should provide attenuation of scattered radiation arising from the collimator or filter. 63 Source-to-skin distance for intraoral radiography shall be at least 20 cm and preferably should be at least 30 cm. 64 Rectangular collimation of the x-ray beam shall be used routinely for periapical and bitewing radiography, and should be used for occlusal radiography when imaging children with size 2 receptors 65 Occupationally-exposed personnel should not routinely restrain uncooperative patients and shall not hold the image receptor in place during an x-ray exposure. 66 Comforters and caregivers who restrain patients or hold image receptors during exposure shall be provided with shielding, e.g., radiation protective aprons, and should hold the film holding device. No unshielded body part of the person restraining the patient shall be in the primary beam

23 67 The stand of a mobile unit shall provide adequate support to the x-ray tube during travel and when the articulating arm is fully extended, and during x-ray exposure. The wheels or the casters shall be equipped with a foot brake to prevent motion of the unit during exposure. 68 Only the patient and operator shall be in the area during an exposure unless special circumstances do not allow this. 69 The tube head shall achieve a stable position, free of drift and oscillation, within 1 s after its release at the desired operating position. Drift during that 1 s shall be no greater than 0.5 cm. 70 Operators of hand-held x-ray equipment shall have the physical ability to hold the system in place for multiple exposures. 71 Manufacturers should provide a training program for users of hand-held equipment to emphasize the appropriate safety and positioning aspects of their unit. 72 Operators shall store hand-held x-ray equipment such that it is not accessible to members of the public when not in use. 73 Manufacturers of hand-held x-ray equipment shall incorporate either hardware or software interlocks on their devices to prevent unauthorized use. Hardware interlocks may include physical keys or locks necessary for operation while software interlocks may include password restrictions. 74 Instructions supplied with hand-held x-ray equipment shall include identification of the areas in which it is safe for the operator to stand during exposures based on the specific protective shielding in the device design. 75 Hand-held x-ray devices shall include a clear, external, nonremovable, radiation protection shield containing a minimum of 0.25 mm lead equivalence between the operator and the patient to protect the operator from backscatter radiation

24 76 The operator of a hand-held x-ray unit shall not be required to wear a personal radiation protective garment. 77 Rectangular collimation shall be used with hand-held devices whenever possible. 78 The x-ray beam for rotational panoramic tomography shall be collimated such that its vertical dimension is no greater than that required to expose the area of clinical interest and shall not exceed the size of the image receptor. 79 The fastest imaging system consistent with the imaging task (equal to or greater than ANSI 400 speed, or digital) shall be used for all panoramic radiographic projections Panoramic machines shall be on a dedicated electrical circuit The fastest imaging system consistent with the imaging task (ANSI 400 speed or greater, or digital) shall be used for all cephalometric radiographic projections. 82 X-ray equipment for cephalometric radiography shall provide for asymmetric collimation to limit the beam to the area of clinical interest. 83 Filters for imaging the soft tissues of the facial profile together with the facial skeleton shall be placed between the patient and at the x-ray source rather than at the image receptor. 84 CBCT should be used for cross sectional imaging as an alternative to conventional computed tomography when the radiation dose of CBCT is lower and the diagnostic yield is at least comparable. 85 CBCT examinations shall use the smallest field of view (FOV) and technique factors that provide the lowest dose commensurate with the clinical purpose. 86 CBCT examinations shall not be obtained solely for the purpose of producing simulated bitewing, panoramic, or cephalometric images

25 87 CBCT shall not be used as the primary or initial imaging modality when an alternative lower dose imaging modality is adequate for the clinical purpose. 88 CBCT examinations shall not be used for routine or serial orthodontic imaging. 89 Manufacturers should develop P KA values for CBCT acquisitions and provide conversion coefficients or other dose metrics necessary for the calculation of effective dose in order to allow an estimate of risk for each acquisition. 90 Only hand-held dental x-ray devices cleared by FDA for sale in the United States shall be used. 91 Regulations preventing the user from holding the x-ray unit should not be applied to equipment cleared by FDA that is designed to be hand-held. 92 States should develop and apply specific regulations for the dental uses of CBCT. 93 Radiation safety training shall be provided to all dental staff and other personnel, including secretaries, receptionists, and laboratory technologists. This training shall be commensurate with the individual s risk of exposure from ionizing radiation. 94 Every person who operates dental x-ray imaging equipment or supervises the use of such equipment shall have current training in the safe and efficacious use of such equipment. 95 The dentist should regularly participate in continuing education in all aspects of dental radiology, including radiation protection. 96 Opportunities should be provided for auxiliary personnel to obtain appropriate continuing education credits. 97 The manufacturer shall provide training pertaining to the safe operation of the hand-held unit

26 98 The manufacturer of hand-held dental x-ray units shall provide information suitable for the qualified expert regarding radiation leakage, backscatter radiation, and the importance of the integral radiation shield. 99 The predoctoral dental curricula shall include didactic and clinical education on physics of CBCT image production, artifacts that can lead to image degradation, indications, and limitations of CBCT in dental practice, and the effects of acquisition parameters on radiation dose. 100 Postdoctoral or clinical residency curricula shall expand upon the predoctoral education and include discipline-specific indications and limitations of CBCT imaging and the effects of acquisition parameters on radiation dose. 101 Dental practitioners who own CBCT units or use CBCT data sets in their clinical practice and who have not received CBCT education as part of their predoctoral or postdoctoral education shall acquire equivalent understanding of the basic radiation safety aspects of CBCT imaging and sufficient knowledge in the indications and limitations of CBCT imaging. 102 Dental personnel who operate CBCT units shall be adequately trained in the proper operation and safety of the units. They should demonstrate adequate knowledge of different protocols affecting the image quality and radiation dose to the patient. 103 Prior to working with CBCT equipment, operators shall receive education on the basics of CBCT technology, the risks associated with radiological imaging, and training on the effective operation of CBCT equipment. This education must include principles of CBCT image formation, equipment settings and their impact on patient dose, and common artifacts associated with CBCT images

27 104 All operators shall complete training on each individual CBCT system they will be using, as provided by the manufacturer. This device specific training must include patient positioning, the range of user selectable exam settings, and their effect on dose, protocol selection, image processing options, and periodic maintenance schedules. 105 A qualified expert shall have appropriate training and mentored experience in the evaluation of dental CBCT facilities prior to functioning independently. 106 Every person who operates CBCT equipment, supervises the use of CBCT equipment or tests and evaluates the functions of CBCT equipment shall have ongoing continuing education in the safe and effective use of that equipment

28 Introduction Radiology is an essential component of dental diagnosis. While available data clearly show that ionizing radiation at modest to high doses produces biological damage, there is considerable uncertainty and disagreement regarding the existence and nature of biological damage at very low doses such as used in dental diagnosis except for some cone beam computed tomography (CBCT) examinations. Given the billions of dental exposures annually across the population, it is only prudent to address the controversy by assuming that there is a small but real risk of harm, and to promulgate recommendations that foster safe and effective use of diagnostic dental imaging to protect patients, staff and the public from radiogenic harm. Furthermore, the practitioner may reasonably expect that the health benefit to the patient from dental radiographic examination will outweigh any potential risk from radiation exposure provided that the: dental radiographic examination is clinically indicated and justified; radiographic technique is optimized to ensure images adequate for diagnosis at the lowest dose consistent with this aim; and principles outlined in this Report are followed to minimize exposure to the patient, staff, and the public Office design, imaging and associated equipment, and procedures that minimize patient exposure will also reduce exposure to the operator, other staff, and the public. Additional measures, however, may be required to ensure that doses to operators and the public are within limits established by regulatory bodies. Doses to all should be kept as low as reasonably achievable (i.e., the ALARA principle) (NCRP, 1990). For operators and the public, the ALARA principle encourages further reduction of doses that are already below regulatory limits. The concept may be extended to patients, for whom dose limits do not apply. In this case, however, we must assure that the imaging chain is optimized such that lower radiation doses are sufficient to produce images of clinically acceptable quality. The process of balancing image quality with radiation dose is known as optimization

29 Purpose The main objective of this Report is to present rationale, methods, and procedures for radiation protection of patients, staff in the dental office and the public. The goals are: eliminate unnecessary radiation exposure to the patient by assuring that images are obtained only when justified and necessary; 2. assure that imaging equipment operates properly; 3. assure that images are of diagnostic quality; and 4. limit radiation exposure and meet the ALARA principle for staff and for patients This Report makes a number of recommendations to achieve these goals in the dental office Scope This Report provides guidelines for radiation protection regarding the use of x rays in dental practice. It replaces the National Council on Radiation Protection and Measurements Report No. 35 (NCRP, 1970) and Report No. 145 (NCRP, 2003) in their entireties. It presents recommendations regarding the optimization and clinically appropriate use of dental x-ray equipment, as well as recommendations for radiation protection surveys, and monitoring of personnel. Sections are included as specific guidance for dentists, their clinical associates, and qualified experts conducting radiation protection surveys, equipment performance evaluations, and determining facility shielding and layout designs; discussions of administrative and educational considerations are also included. Additionally, there is guidance for equipment designers, manufacturers, and service personnel. Basic guidance for dentists and their office staff are contained in the body; technical details are provided in the appendices The target audience may not have easy access to related documents, therefore this Report is intended to serve as a complete reference, providing sufficient background and guidance for most dental imaging applications. Additional details regarding general medical and related topics 29

30 may be found in other reports of the NCRP (1976; 1988; 1989a; 1989b; 1990; 1992; 1993a; 1993b; 1997; 1998; 2000; 2001; 2004; 2005; 2008; 2009; 2012a; 2012b; 2013) This report is to focuses particularly on those imaging procedures commonly performed in dental facilities, including film, digital and hand-held intraoral radiography, and panoramic, cephalometric, and cone beam computed tomography exams, and their associated equipment and techniques. Except as otherwise specified, the recommendations in this Report apply to these equipment and procedures. Other procedures of oral and maxillofacial radiology that are not generally practiced in the dental office and that require more sophisticated equipment are subject to the requirements and recommendations for medical radiology (NCRP, 1989a; 1989b; 2000; 2013), and will not be specifically addressed in this report Radiation Protection Philosophy Biological effects of ionizing radiation fall into two classes. Tissue reactions (also known as deterministic effects) and stochastic effects (Appendix I). Tissue reactions occur in all individuals who receive a sufficiently high dose, i.e., exceeding some threshold. Examples of these effects are acute radiation sickness, cataracts, skin burns, and epilation. Their severity increases with increasing dose, and there is a threshold dose below which no clinicallysignificant tissue reactions occur. Stochastic effects, such as cancer, are all-or-nothing effects: either a radiation-induced cancer occurs or it does not, and its severity is not dependent on radiation dose. The probability of its occurrence increases with increasing dose, implying the absence of a threshold The basic goal of radiation protection is to prevent in exposed individuals the occurrence of tissue reactions and to reduce the risk for stochastic effects to an acceptable level when benefits of that exposure are considered (NCRP, 1993a; 2004) Achievement of this goal requires two interrelated activities: (1) efforts to ensure that no occupationally exposed individual or member of the public receives doses greater than the limits recommended for occupational and public exposures; and (2) efforts to ensure that patient doses 30

31 are ALARA. In most applications, ALARA is simply the extension into health care of good radiation protection programs and practices that have traditionally been effective in keeping the average of individual exposures of monitored workers well below the limits. Cost-benefit analysis is applied to measures taken to achieve ALARA goals. For each source or type of radiation exposure, it is determined whether the benefits outweigh the costs. Second, the relation of cost to benefit from the reduction or elimination of that exposure is evaluated. Frequently costs and benefits are stated in disparate units. Costs may be in units such as adverse biological effects or economic expenditure. Benefits may be in units such as disease detected or lives saved. Three principles provide the basis for all actions taken for purposes of radiation protection in diagnostic imaging. These principles are applied differently for patients, occupationally exposed persons, and the public. They are Justification: The benefit of radiation exposure outweighs its accompanying risks; 2. Optimization of protection: Total exposure remains as low as reasonably achievable (ALARA); 3. Application of dose limits: For occupational and public exposure, dose limits are applied to each individual to ensure that no one is exposed to an unacceptably high risk All three of these principles are applied to evaluation of occupational and public exposure. Only the first two apply to exposure of patients. Dose limits do not apply to patients because medical and dental exposures are obtained for diagnostic purposes that benefit the patient. The primary objective of medical and dental imaging is to ensure that the health benefit exceeds the risk to the patient from that exposure NCRP has established recommended dose limits for occupational and public (nonmedical) exposure (Table 2.1) (NCRP, 2004b). Limits have been set below the estimated human threshold doses for tissue reactions. NCRP assumes that for radiation protection purposes, the risk of stochastic effects is proportional to dose without threshold, throughout the range of dose and dose rates of importance in routine radiation protection (NCRP, 1993). This principle was used to set dose limits for occupationally-exposed individuals such that estimated risks of stochastic 31

32 537 TABLE 2.1 Recommended dose limits (NCRP, 2004b). a Basis Dose Limit Occupational Stochastic effects 50 msv annual effective dose [10 msv (x) age (y) = cumulative effective dose] Deterministic effects (tissue reactions) 150 msv annual equivalent dose to the lens of the eye 500 msv annual equivalent dose to skin, hands, and feet Public b Stochastic effects Tissue reactions 1 msv annual effective dose for continuous or frequent exposure 5 msv annual effective dose for infrequent exposure 15 msv annual equivalent dose to the lens of the eye 50 msv annual equivalent dose to the hands, skin, hands, and feet Embryo and Fetus 0.5 msv equivalent dose in a month from occupational exposure of the mother once pregnancy is declared 538 a The appropriate dose limits for adult students (i.e., age 18 y or older) in dental, dental 539 hygiene, and dental assisting educational programs depend on whether the educational entity classifies the student as occupationally exposed or not. Additional guidance for radiation protection practices for educational institutions is given in NCRP (2007). Dose limits for students under 18 y of age correspond to the limits for members of the public (NCRP, 2004b). b These limits do not apply to exposures for medical or dental diagnosis or treatment. 32

33 effects are no greater than risks of occupational injury in other vocations that are generally regarded as safe Dentists shall use x-ray equipment and procedures in a manner that ensures compliance with both the recommendations in this Report and the requirements of their state or local jurisdictions. When there is conflict between the recommendations in this Report and applicable legal requirements, the more rigorous shall take precedence

34 General Considerations All persons are exposed to radiation in their daily lives (NCRP, 1987a; 1987b; 1987c; 1987d; 1989c; 1989d, 2009). NCRP has estimated the average total annual effective dose per individual in the U.S. population in 2006 from all sources of radiation in the United States as 6.2 msv (Figure 3.1). Approximately 3 msv of this arises from naturally-occurring sources; these sources have been present since the beginning of the Earth. Medical imaging contributes 48 % of the annual effective dose per individual. This represents an increase by a factor of 2.2 from the early 1980s to 2006, and is primarily due to increased utilization of the medical modalities of computed tomography, nuclear medicine, and interventional fluoroscopy (NCRP, 2009) Dental radiation is a minor contributor to total population burden. However, the increasing use of cone beam CT imaging, increases in conventional dental imaging, and revisions in the ICRP Tissue Weighting Factors (ICRP, 2007) results in a growing contribution of dental imaging to the population effective dose. Thus, appropriate measures are necessary to maintain dental radiation exposures ALARA Dose Limits The Council has recommended annual and cumulative dose limits for individuals from occupational radiation exposure, and separate annual dose limits for members of the public from sources of man-made radiation (Table 2.1) (NCRP, 1993a). The dose limits do not apply to diagnostic or therapeutic exposure of the patient in the healing arts. (Some states may have adopted different occupational limits.) The cumulative limit for occupational dose is more restrictive than the annual limit. For example, an individual who begins at 18 y of age to receive annual occupational effective doses of 50 msv will in 4 y receive 200 msv, approaching the cumulative limit of 220 msv at 22 y of age. At that point, occupational exposure to that individual would be constrained by the cumulative, not the annual limit. That is, the individual would then be limited to a cumulative effective dose at the average rate of 10 msv y -1, with a maximum rate of 50 msv in any 1 y. The 34

35 Fig Percent contribution of various sources of exposure to the total collective effective dose (1,870,000 person-sv) and the total effective dose per individual in the U.S. population (6.2 msv) for Percent values have been rounded to the nearest 1 %, except for those <1 % (NCRP, 2009). Conventional dental imaging accounts for 0.25 % of the dose from all medical imaging (White and Pharoah, 2014); however, the contribution of cone beam CT imaging to the computed tomography dose (medical) is at present unknown, and likely increasing

36 duties of any individual who approaches the annual or cumulative limit may be changed so the limit is not exceeded. It should be stressed that these are occupational exposures and not exposures from medical diagnosis or treatment Average dental occupational exposures are usually only a small fraction of the limit and are less than most other workers in the healing arts (Table 3.1) (Kumazawa et al., 1984). Occupational exposures have been declining (Figure 3.2) over recent decades in workers in both the healing arts in general and dentistry in particular (HSE, 1998; Kumazawa et al., 1984; UNSCEAR, 2000). It seems reasonable to conclude that no dental personnel will receive occupational exposures exceeding the limit as long as proper facility design, equipment performance, and operating procedures are implemented Facilities are designed, operated, and monitored such that no individual member of the public receives a dose in excess of the recommended limit. Therefore, members of the public are not monitored While there are no recommended dose limits for medically necessary radiation exposure, the ALARA principle of radiation protection optimization can be applied to patients as well. For dental exposures of patients, The NCRP agrees with the statement by ICRP (2007b, paragraph 70): The optimization of radiological protection means keeping the doses as low as reasonably achievable, economic and societal factors being taken into account, and is best described as management of the radiation dose to the patient to be commensurate with the [dental] purpose. That ICRP publication clarifies the goal of the ALARA principal in medical [dental] imaging (paragraph 47): In medicine [dentistry] the requirement is to manage the radiation dose to the patient to be commensurate with the medical [dental] purpose. The goal is to use the appropriate dose to obtain the desired image or desired therapy Facility design, x-ray equipment performance, and operating procedures shall be established to maintain patient, occupational and public exposures as low as reasonably achievable (ALARA). When new equipment is installed or substantially different practices are

37 638 TABLE 3.1 Occupational doses in the healing arts, United States, a Occupation Number of Workers Mean Annual Whole-Body Dose (msv) Total b Exposed c Total b Exposed c Hospital 126,000 86, Medical offices 155,000 87, Dental (offices) 259,000 82, Podiatry 8,000 3, Chiropractic 15,000 6, Veterinary 21,000 12, Total 584, , a Kumazawa et al. (1984). b All workers with potential occupational exposure. c Workers who received a measurable dose in any monitoring period during the year

38 Fig Decline in mean occupational doses over recent decades, for workers in all healing arts combined and dentistry. U.S. data at 5 y intervals from 1960 to 1980 plus that projected for 1985 were reported as dosimeter readings (Kumazawa et al., 1984). World estimates from 1975 to 1995 were reported as effective doses and are plotted at each 5 y interval (UNSCEAR, 2000)

39 implemented, staff shall wear personal radiation badges for 1 y to ascertain the level of typical radiation doses (Section 4.5.5) All individuals engaged in dentomaxillofacial imaging shall meet the following radiation protection limits: Recommendation 1. No individual worker shall receive an occupational effective dose in excess of 50 msv in any 1 y Recommendation 2. The numerical value of the individual worker s life-time occupational effective dose shall be limited to 10 msv times the value of his or her age in years. Occupational equivalent doses shall not exceed 0.5 msv in a month to the embryo or fetus for pregnant individuals, once pregnancy is known Recommendation 3. Mean nonoccupational effective dose to frequently or continuously exposed members of the public shall not exceed 1 msv y -1 excluding doses from natural background and medical care); infrequently exposed members of the public shall not be exposed to effective doses >5 msv in any year NOTE: NCRP is presently engaged in a major review of NCRP Report No. 116, Radiation Protection Guidance for the United States. NCRP may issue a new report with different occupational and public dose limits that would supersede those specified in Recommendations 1 to 3 above. Ultimately, practitioners must comply with applicable federal and state regulations regarding exposure of workers and the public Role of Dental Personnel in Radiation Protection ALARA requires optimizing the practices of all dental personnel who are involved in prescription, exposure, processing, evaluation, and interpretation of dental images. This Section describes the roles of each

40 The Dentist In most dental facilities a single dental practitioner is responsible for the design and conduct of the radiation protection program. In large facilities, such as dental educational institutions, the authority and responsibility for design and oversight of the radiation protection program may be delegated to a specific employee with special expertise in the field. This individual is designated the radiation safety officer. The dentist in charge, in consultation with the radiation safety officer (if that person is someone other than the dentist) and with a qualified expert, is responsible for implementing the radiation protection program, which includes (NCRP, 1990; 1998) establishing, reviewing, and documenting radiation protection procedures; instructing all dental staff in radiation protection; implementing radiation surveys and recording results and corrective actions; establishing the monitoring of personnel, if required; ensuring that all radiation protection features are functional and the required warning signs are posted; implementing and monitoring the ALARA principle; and implementing and documenting quality assurance (QA) and quality control (QC) procedures Guidance on developing appropriate radiation protection programs for a dental office can be found in most contemporary oral radiology textbooks (White and Pharoah, 2014) Recommendation 4. The dentist (or, in some facilities, the designated radiation safety officer) shall establish and periodically review a radiation protection program. The dentist shall seek guidance of a qualified expert in this activity The dentist is qualified by education and licensure to prescribe and perform radiographic examinations and to evaluate and interpret the images produced

41 Recommendation 5. The dentist shall employ published, evidence-based selection criteria when prescribing radiographs Additional details concerning selection criteria are found in Sections and Auxiliary Personnel In most dental facilities the staff involved in radiologic procedures consists of registered dental hygienists and dental assistants who may or may not be certified. Registered hygienists and certified assistants are trained and credentialed to perform radiological examinations, process film, and digital images and evaluate them for quality (NRPB, 2001). In some states noncertified assistants may be credentialed for these procedures upon completion of approved training Recommendation 6. Radiological procedures shall be performed only by dentists or by legally qualified and credentialed auxiliary personnel The Qualified Expert This individual is qualified by education and experience to perform advanced or complex procedures in radiation protection that generally are beyond the capabilities of most dental personnel (NRPB, 2001). These procedures include facility design to provide adequate shielding for protection of the occupationally exposed and the public, inspection and evaluation of performance of x-ray equipment, evaluation of and recommendations for radiation protection programs, and to assist in optimizing image quality and patient radiation dose. Usually possessing an advanced degree in medical physics or a similar field, this individual is usually certified by the American Board of Radiology, the American Board of Medical Physics, or equivalent. Care must be taken to ensure that the qualified expert s credentials include knowledge and familiarity with dental radiologic practices. Some otherwise highly qualified experts may have little experience in dental radiological practices. (Some states credential or license these individuals.) The principal responsibility of this person is to serve as a consultant to the dentist. 41

42 The qualified expert adds essential value to the dental practice by providing expertise in radiation shielding design, radiation safety for the staff and general public, applicable regulatory and accreditation requirements, and establishing the quality control program. Specifically, the qualified expert: Performs a pre-installation radiation shielding design and plan review. Performs acceptance testing [equipment performance evaluation (EPE)] and a postinstallation radiation protection survey. Initiates the quality control program by evaluating the initial characteristics of the x-ray beam, measuring patient exposures, and assessing image quality. Establishes the quality control program by advising on the individual elements of the QC program, procedures to be followed, the qualifications of personnel, expected ranges of results, and actions to be taken when results are beyond the expected ranges. Quality control programs for dental offices are described in oral and maxillofacial radiology textbooks (White and Pharoah, 2014). Compares measured metrics of dose to the patients with published Diagnostic Reference Levels and Achievable Doses. Advises on the x-ray exposure parameters (e.g., exposure time, tube potential, field size or collimation, and other technique factors) to be used to achieve optimum image quality and minimal radiation dose (optimization) Recommendation 7. The qualified expert should provide guidance for the dentist or facility designer in the layout and shielding design of new or renovated dental facilities and when equipment is installed that will significantly increase the air kerma incident on walls, floors, and ceilings Recommendation 8. The qualified expert shall provide guidance for the dentist regarding establishment of radiation protection policies and procedures

43 Electronic Image Data Management Secure management of patient image data is an important aspect of quality assurance and overall proper care of patients. Thus, image data must be stored in a way that provides robust security, allows routine access for the practitioner or designee, and enables secure transmission of the image data to other practitioners for consultation or at the request of the patient The electronic health record in a dental office should allow for interaction with a properly configured picture archiving and communication systems (PACS) or should have as a subset a good PACS within its architecture. The PACS is a major component in radiology in dentistry and medicine and is the backbone of digital imaging. It is recommended that images that are stored in the PACS system be in the Digital Imaging and Communications in Medicine (DICOM) standard format. DICOM is the standard for the communication and management of medical imaging information and related data. If a practitioner is using a proprietary storage and communication system that comes with their x-ray equipment, this system should fulfill the basic functions of a PACS system and should store it s electronic image data in the DICOM format The ability of PACS systems to share imaging data can benefit patients by reducing the likelihood that an x-ray exam is needlessly repeated.. A lack of data sharing in dental imaging is a major problem and often responsible for repeated x-ray exposures because many data systems presently in use do not integrate well with other systems or products, often requiring repeated exposures The benefits of a good PACS system include: secure storage of images; 2. organization of images; 3. archiving of current and older images; 4. easy workflow organization; 5. distribution of images and associated metadata (e.g., image interpretation, photos, histopathologic findings); 43

44 restoration of lost d to prevent downtime and prevent the need to retake images; and 7. possible web access to images and data. The PACS should allow for: 1. high quality display of images; 2. appropriate adjustment of images (post processing, i.e., window and level adjustment); 3. support for multimodality images; 4. customizable protocols and display of technical factors; 5. the use of templates to create structured reports which include estimated radiation dose to the patient; 6. built in quality assurance tools; 7. automatic backups; 8. retrieval of accessed data; 9. easy upgrading; 10. compatible with open standards; 11. easy integration with electronic health records; and 12. easy integration of third party voice transcription software. Data management in dentistry and medicine falls under the purview of the Health Insurance Portability and Accountability Act of 1996 (HIPAA), with the primary goal of protecting the confidentiality and security of the electronic health care information of patients. Failure to comply with HIPAA may result in civil and criminal penalties. Recommendation 9. To avoid unnecessary repeat exposures due to lost images or redundant examinations, the electronic image data management system shall provide for secure storage, retrieval, and transmission of image data sets Recommendation 10. All digital images acquired shall be retained in the patient s electronic record. Recommendation 11. All digital images should be backed up offsite electronically in a separate, safe, and secure location at regular intervals. 44

45 Radiation Protection in Dental Facilities Radiation protection recommendations specific to the dental facility are provided in this Section. Technical details are found in the appendices General Considerations Facilities are occupied by patients, dentists, clinical and nonclinical staff, and the public. Therefore, facilities must be designed with the radiation protection and safety of all of these groups From a radiation protection perspective, dental x-ray equipment (both permanently mounted and hand-held equipment) must be installed and utilized so that patient and personnel exposures are maintained ALARA, while simultaneously providing the image quality necessary to meet the clinical needs. An experienced x-ray equipment provider may suggest possible configurations to meet the needs and limitations of each practice environment. However, the qualified expert should review the anticipated workload and proposed installation plan before renovation, construction, and installation begins, to assure that each individual room configuration will meet local regulatory requirements and the ALARA principle. The shielding principles used may be found in NCRP Report No. 147 (NCRP, 2004a) Perhaps the most important and often overlooked requirement of an equipment installation plan is that, after positioning the patient and the imaging equipment, the operator must be able to see and hear the patient while initiating the x-ray exposure. This is essential to assure that the patient (or the x-ray equipment) has not moved since positioned by the operator. This may be accomplished by the operator standing in a doorway (if the distance is adequate for radiation protection), viewing the patient through a window designed to meet the radiation protection goals, mirror or video monitoring system, or any other means that assures continuous visual and audible communication between the patient and the operator

46 Depending on the room size, workload, and x-ray modality used, for typical intraoral dental radiography installations, it is common (but not always true) that commercial construction (two layers of 5/8 inch gypsum wallboard, or GWB) provides sufficient radiation protection, since GWB attenuates x-radiation in the dental diagnostic range. High workloads, small rooms and proximity to other persons may increase the shielding requirements. The qualified expert should perform a pre-installation shielding design and a post-installation shielding survey Shielding Design Shielding design must be included in facility planning (before floor plans are completed) to ensure that neither occupational nor public doses exceed established limits. The qualified expert may present more than one shielding design for a facility. Each design may include office layouts, equipment locations, doorway positions, construction of partitions, etc. Construction costs vary directly with the magnitude of dose reduction. With innovative design, dose reductions can be achieved at little or no cost and without adverse impact on patient care (i.e., the ALARA principle) Recommendation 12. The qualified expert should perform a pre-installation radiation shielding design and plan review, to determine the proper location and composition of barriers used to ensure radiation protection in new or renovated facilities, and when equipment is installed that will significantly increase the air kerma incident on walls, floors, and ceilings Recommendation 13. The qualified expert shall perform a post-installation radiation protection survey to assure that radiation exposure levels in nearby public and controlled areas are ALARA and below the limits established by the state or other local agency with jurisdiction The essential radiation safety requirement of structural shielding is that the exposure to persons near the x-ray equipment shall be maintained ALARA, and within specific requirements 46

47 set by the state or other jurisdiction. The following general considerations apply to most dental imaging facilities: Due to the relatively low levels of scattered radiation produced during most intraoral, cephalometric, and panoramic x-ray installations, it is common (though not always true) that the shielding provided by drywall (GWB) used in routine construction will provide sufficient radiation shielding without the need for additional lead or other special shielding materials. The location of walls and doors are an essential component of the room shielding configuration. 2. In the design of x-ray shielding, dentists, dental hygienists, and dental assistants are considered to be occupationally exposed personnel. All other persons should be considered members of the general public. 3. To minimize unnecessary radiation exposure due to repeated exams, the operator shall maintain visual and audible contact with the patient, or with the care provider of a nonverbal patient, during each x-ray exposure. The qualified expert should keep this in mind and specify the recommended location of the operator during each exposure. 4. While it is common to install CBCT systems to replace previously existing panoramic dental radiographic systems, CBCT systems produce substantially more scattered radiation than panoramic dental units (typically by at least a factor of 10). Hence, shielding or location of panoramic rooms will often be insufficient for a CBCT system. 5. Some dental facilities equip and utilize a special x-ray room for multiple x-ray imaging examinations: intraoral, cephalometric, panoramic, or CBCT imaging. Cumulative radiation exposures resulting from representative weekly workloads in each modality must be considered when designing shielding for such a room Detailed discussions of all aspects of shielding design for dental facilities, including CBCT facilities, are found in Appendix D Recommendation 14. The qualified expert should assess each facility individually and document the recommended shielding design in a written report. 47

48 Recommendation 15. The qualified expert should consider the cumulative radiation exposures resulting from representative workloads in each modality when designing radiation shielding for rooms in which there are multiple x-ray machines Some facilities include rooms with multiple x-ray machines. Shielding design for such rooms assumes that only one patient is imaged at any one time Recommendation 16. The facility shall establish administrative controls that assure no more than one patient is in an x-ray room with multiple x-ray machines during any x- ray exposure Equipment Performance Evaluations and Radiation Protection Surveys Initial and periodic equipment performance evaluations (EPE) are the responsibility of the qualified expert. This testing is performed to determine compliance with laws and regulations governing the safety and performance of the equipment, assure that patient doses and image quality are optimized, and verify the validity of the technique charts. In addition, this evaluation includes assuring that the equipment is being used in a manner compatible with standards of good radiologic practice Newly installed equipment also must comply with all applicable federal performance standards (FDA, 2015). While this compliance is certified by the equipment installer, the initial performance of new equipment is determined by the qualified expert through acceptance testing. Acceptance testing ensures that the new equipment performs as specified in the agreement between the buyer and seller, and may address equipment performance beyond the scope of the federal performance standard. Any deviations are reported to the dentist, who is responsible for corrective action Recommendation 17. A qualified expert shall evaluate x-ray equipment to ensure that it is in compliance with applicable governing laws and regulations. 48

49 Dental x-ray facilities must have a radiation protection survey before the imaging equipment is used to assure that the radiation protection is sufficient to meet the design goals and regulatory limits. In addition, a survey shall be made after any change in the installation, workload, or operating conditions that might significantly increase occupational, patient, or public exposure (including x-ray machine service or repair that could affect the x-ray machine output or performance) These surveys and EPEs are performed by a qualified expert and should be performed at regular intervals. This interval should not exceed 4 y for intraoral, panoramic or cephalometric equipment, and should not to exceed 2 y for CBCT units The essential elements of a survey and EPE performed by a qualified expert should include: radiation safety survey; 2. occupational radiation exposure assessment; 3. evaluation of image receptor performance and dose; 4. evaluation of the x-ray generator and radiation output characteristics; 5. evaluation of beam collimation and filtration; and 6. clinical image quality Detailed descriptions of these survey elements and a sample CBCT radiation protection survey can be found in Appendices D and H Recommendation 18. All new dental x-ray installations shall have a radiation protection survey and equipment performance evaluation carried out by, or under the direction of, a qualified expert Constancy testing is a periodic equipment performance evaluation carried out by a qualified expert to determine whether x-ray producing and imaging systems continue to meet performance 49

50 standards established during acceptance testing. If acceptance testing data is unavailable, the qualified expert uses manufacturer s specifications as performance criteria Image quality and dose in dental radiography can be assessed by the use of devices that are mailed to dental intraoral facilities, exposed, and returned to the vendor for evaluation. These may be of particular utility for monitoring dental facilities in remote locations and facilities that are visited by a QMP less often than annually and for regulatory oversight Recommendation 19. Equipment performance evaluations shall be performed by a qualified expert at regular intervals thereafter, preferably at intervals not to exceed 4 y for facilities only with intraoral, panoramic or cephalometric units. Facilities with CBCT units shall be evaluated every 1 to 2 y Signage Some states require clearly visible signage in the patient care areas. This may include posted statements identifying radiation use areas or in imaging rooms instructing patients to notify dentist and staff if they are or may be pregnant Diagnostic Reference Levels and Achievable Doses Diagnostic reference levels (DRLs) and achievable doses (AD) can be used as guidance in optimizing the doses to patients from dental imaging examinations. In particular, DRLs can be used to help ensure that patient radiation doses are not grossly excessive NCRP Report No. 172 (NCRP, 2012) describes DRLs and ADs and their uses, describes the history of their development, and provides suggested values for the United States for a variety of imaging modalities and procedures. In particular, it defines a DRL as: A radiation dose level serving as an investigational level. When doses exceed the DRL the reasons for the higher doses should be investigated. A process known as optimization is used 50

51 to assure that the image quality is adequate for the clinical task and that the patient doses are appropriate. The diagnostic reference level is typically set at the 75 th percentile of the distribution of dose metrics from a representative sample of facilities And an achievable dose as: A dose which serves as a goal for optimization efforts. This dose is achievable by standard techniques and technologies in widespread use, while maintaining clinical image quality adequate for the diagnostic purpose. The achievable dose is typically set at the median value of the dose distribution Dose metrics used to generate DRLs and ADs may be based upon dose measurements made by qualified experts or others during simulated examinations without the presence of a patient or from dose metrics recorded by the x-ray imaging systems from actual patient examinations. To date, DRLs provided by the NCRP for use in the United States have been based, primarily, upon data collected by the former method (NCRP, 2012b). There are advantages and disadvantages to both methods. For patient examination-based DRLs, inaccuracy in the calibration of the dose measurement system of the imaging device is a potential source of error. Another source of variability in patient measurements is the variability in the size of the patient. Radiation exposures can vary substantially for the same examination depending on the thickness of the patient for the same body part. Alternatively, it takes considerably more effort to measure doses than to simply record dose metrics from patient examinations There are few sources of data today in the United States for use in determining DRLs and ADs. The U.S. Food and Drug Administration s (FDA) Center for Devices and Radiological Health (CDRH), the Conference of Radiation Control Program Directors (CRCPD), and many states in the United States collaborate in the Nationwide Evaluation of X-ray Trends (NEXT) program. Data on the radiation exposures for selected diagnostic x-ray exams are collected from nationally representative samples of clinical facilities in the United States. The initial such NEXT survey of dental imaging was conducted in 1999; its findings were initially reported in 51

52 (Moyal, 2007). At the time of writing, another NEXT survey of dental imaging was recently completed (Farris and Spelic, 2015) Another potential source of data for DRLs and ADs is a registry that would automatically collect dose metrics from dental examinations. The American College of Radiology maintains a dose registry for diagnostic CT and other examinations. It would be extremely useful to have the ability to generate DRLs and ADs for CBCT examination in dentistry from a dental dose registry There are disadvantages to this process for creating and using DRLs and ADs in the United States. In particular, the NEXT process takes time and considerable effort to collect and analyze the dose data from a large number of institutions. This can limit the number of examinations for which DRLs and ADs are available and can also cause the DRLs and ADs to be based on data from many years ago, which may not be fully relevant to current usage and technology For examinations for which appropriate and recent DRLs for the United States are not available, an option is to use DRLs from other countries (e.g., Hart et al., 2012; Holroyd, 2011; 2013). Another option is to compare the doses from a facility s protocols with dose data collected by other reputable institutions. In either case, bias can be introduced due to differences in practice Each dental facility should compare its dose metrics against DRLs and ADs. When qualified experts or state inspectors test dental imaging systems, they should collect dose data in a manner suitable for comparison with DRLs and ADs. For imaging systems that display dose data, these data should be compared with DRLs and ADs Careful consideration should be given when there are different technologies in use for imaging. For example, currently, intra-oral radiography is being performed with film, photostimulable storage phosphor (PSP) plates, and direct digital radiography image receptors. The currently available DRLs and ADs are largely due to data from facilities using film. Facilities with direct digital receptors may presume that their doses are optimized if they are less 52

53 than these DRLs and similar to the ADs, but in fact their doses may be higher than needed for clinically-adequate images The creation of interim DRLs and ADs, published in the literature from studies involving small numbers of reputable institutions, is recommended. Recommendation 20 Diagnostic Reference Levels and Achievable Doses should be developed for dental CBCT imaging Recommendation 21. Each dental facility should record and track indicators of patient dose, such as entrance air kerma and associated technique factors Recommendation 22. Each dental facility should compare its doses to DRLs and ADs. In particular, where established methods exist, the qualified expert shall collect dose data suitable for comparison with DRLs and ADs. These data and the results shall be provided in the qualified experts report. For dental imaging systems that provide dose metrics for patient examinations, the dentist or qualified expert should periodically compare medians of these data for 10 clinical examinations appropriate for this purpose with DRLs and ADs Recommendation 23. Organizations such as NCRP, U.S. Food and Drug Administration (FDA), Conference of Radiation Control Program Directors (CRCPD), American Academy of Oral and Maxillofacial Radiology (AAOMR), and American Dental Association (ADA) should strive to provide DRLs and ADs for a variety of dental examinations Optimization of Image Quality and Patient Dose: General Principles Clinical image quality and radiation dose to both patients and staff are the two primary concerns in dental x-ray imaging. The image produced must have sufficient detail and information to assure the practitioner that subtle pathology can be detected. Optimization is the 53

54 balancing of image quality and patient dose. The optimization process is best carried out as a cooperative effort between dentists and qualified experts DRLs and ADs are helpful as part of the optimization process. However, a dose metric found to be less that the appropriate DRL and near the AD does not necessarily mean that the doses are optimized and that image quality is acceptable; in some cases a newer technology (e.g., digital intraoral image receptors) may produce acceptable diagnostic images at doses much lower than the older technology and, if the DRLs and ADs are largely based upon data from the less dose efficient technology, an optimized dose may be considerably less that the AD. Furthermore, optimization can be performed in the absence of DRLs and ADs For film radiography the optimization process starts with using EF-speed film, filling the processor with new developer and fixer, and assuring that the developer is at the temperature specified by the film manufacturer. The film processor should be performing with a consistent level of quality. Once the tube current (ma) and potential (kvp) are determined (either selected by the operator or fixed by the manufacturer), the next step is to optimize the exposure time. Begin with the film manufacturer s recommendation for the average adult patient. On subsequent patients, reduce the exposure time until there is degradation of the image that renders it nondiagnostic; the baseline exposure time for the average adult patient is then set as one time station greater than the setting that produced the degraded, nondiagnostic image. As described in Section 5.1.3, this exposure setting should be incorporated into a technique chart. The chart should also include adjustments from this baseline exposure for children and for large and small adults and adolescents Having established clinically useful exposure settings, one should expose a stepwedge phantom with these settings in order to have a phantom-based image for subsequent quality control checks of film processing and darkroom integrity The steps for digital imaging systems are essentially the same as with film, but without the activities associated with the film processor. A phantom appropriate for the type of digital 54

55 imaging should be used to establish the baseline image. CBCT units have special phantoms which are supplied by the manufacturer (Section 5.2.5) The primary goal of optimization is to select x-ray techniques, and, consequently, patient doses, that produce clinically acceptable images at the lowest dose achievable (ALARA) regardless of whether the image receptor is film or digital Protection of the Patient Potential health benefits to patients from dental x-ray exposure preclude establishment of dose limits for patients. Thus the specific goal of optimization of protection of the patient should be to obtain the necessary clinical information while avoiding unnecessary patient exposure, i.e., the patient exposure is maintained as low as reasonably achievable (ALARA) Selection Criteria. Examination Type and Frequency Elimination of unnecessary radiographic examinations is a very effective method for avoiding unnecessary patient exposure. Guidance on x-ray imaging appropriateness and selection criteria have been developed (FDA/ADA, 2015a; 2015b). Procedures are outlined in Sections through for eliminating unnecessary examinations for both symptomatic patients seeking urgent care and asymptomatic patients scheduled for routine or continuing dental care A clear procedure for reducing the extent and frequency of dental radiographic examinations must be followed when a patient transfers or is referred from one dentist to another. Modern digital imaging and electronic transfer facilitates exchange of information among dentists and other health care providers Recommendation 24. All radiological examinations shall be performed only on direct prescription of the dentist, physician, or other individuals authorized by law or regulation

56 Recommendation 25. Radiographic examinations shall be performed only when patient history and physical examination, prior images, or laboratory findings indicate a reasonable expectation of a health benefit to the patient Recommendation 26. For each new or referred patient, the dentist shall make a good faith attempt to obtain previous, pertinent images prior to acquiring new patient images Symptomatic Patients. When symptomatic patients are seen, the dentist is obligated to provide care to relieve those symptoms and, when possible, eliminate their cause. Radiographs required for that treatment are fully justified, but additional, noncontributory radiographs are not justified. For example, a full-mouth intraoral study is not warranted for emergency treatment of a single painful tooth. However, if treatment of that painful tooth is the first step in comprehensive dental care, then those radiographs required for that comprehensive care are justified Recommendation 27. For symptomatic patients, the radiological examinations shall be limited to those images required for diagnosis and treatment of current disease Asymptomatic Patients. Maintenance of oral health in asymptomatic new patients or those returning for periodic reexamination without clear signs and symptoms of oral disease may require radiographs. Selection criteria that will aid the dentist in selecting and prescribing radiographic examination of these patients have been published (FDA/ADA, 2015a; 2015b). These criteria recommend that dental radiographs be prescribed only when the patient s history and physical findings suggest a reasonable expectation that radiographic examination will produce clinically useful information Recommendation 28. For asymptomatic patients, the extent of radiological examination of new patients, and the frequency and extent for established patients, shall adhere to current published, evidence based selection criteria

57 Administrative Radiographs. Radiographs are occasionally requested, usually by outside agencies, for purposes other than health. Examples include requests from third-party payment agencies for proof of treatment or from regulatory boards to determine competence of the practitioner. In some institutions dental or dental auxiliary students have been required to perform oral radiographic examinations on other students for the sole purpose of learning the technique. Other methods (such as photographs for treatment documentation or image receptor and tube-head placement for radiologic technique training) that do not require exposure to x rays are generally available for providing this information. Dental students can learn to perform x-ray exams using phantoms Recommendation 29. Administrative use of radiation to provide information that is not necessary for the treatment or diagnosis of the patient shall not be permitted Recommendation 30. Students shall not be compelled or permitted to perform radiographic exposures of humans solely for purposes of education Recommendation 31. Candidates shall not be compelled or permitted to perform radiographic exposures of humans solely for purposes of licensure, credentialing or other certification X-Ray Machines All x-ray machines should meet the design specifications and all requirements of the jurisdiction in which they are located. Equipment certified to conform to the federal performance standard (FDA, 2005) will generally meet these requirements. Equipment of recent manufacture (especially that manufactured in Europe) may also conform to IEC standards (IEC, 2012) or regulatory guidance (NRPB, 2001). Specific design considerations are covered in subsequent chapters that address specific imaging modalities Recommendation 32. Personnel responsible for purchase and operation of dental x-ray equipment shall ensure that such equipment meets or exceeds all applicable U.S. federal 57

58 government and state requirements and regulations. In addition, the equipment should conform to current international standards for basic safety and essential performance Examinations and Procedures The general requirements and recommendations in this Report apply to all dental radiological examinations and procedures. This Section, however, presents additional recommendations specific for particular radiographic examinations Intraoral Radiography. Dental intraoral radiographs and chest radiographs have been the most common diagnostic x-ray procedures in the United States. A 2005 to 2006 ADA survey (ADA, 2007), based on practitioner logs, found 308,061,820 periapical images and 423,995,407 bitewing images produced annually in private practices, excluding the military, federal agencies, hospitals, and academic institutions. It is estimated that 493 million intraoral examinations were performed in the United States in 2014 (NEXT 2015). In both cases patient dose per image and resulting radiation detriment are low when compared to other x-ray imaging modalities such as computed tomography. However, the large number of intraoral x-ray procedures performed annually delivers a notable collective dose to the exposed population. Consequently, this requires diligence in optimizing the radiation exposure from these procedures so that unnecessary exposure is avoided and ensuring that such exams are performed only when there is an anticipated benefit to the patient Panoramic Radiography. Panoramic images provide curved-plane tomograms of the teeth and jaws. This imaging method is widely used in dental practice. A 2005 to 2006 ADA survey (ADA, 2007), based on practitioner logs, found 29,552,920 panoramic images produced annually in private practices, excluding the military, federal agencies, hospitals, and academic institutions. The major advantages are rapid acquisition of a single image encompassing the entire dental arches and their supporting structures. The zone of sharp focus ( focal trough ) is limited and varies with manufacturer and model. It is designed to accommodate average adults; a few machines allow adjustment to patient dimensions. Patient positioning is critical and varies with manufacturer and model. Some machines allow only limited adjustment of beam technical 58

59 factors such as image receptor speed, patient thickness and tube current. Effective dose to the patient for a single panoramic image is approximately equal to that from two to four intraoral images, both using state-of-the-art technique (Gibbs, 2000; White and Pharoah, 2014) Cephalometric Radiography. The cephalometric technique provides geometrically reproducible radiographs of the facial structures. A 2005 to 2006 ADA survey (ADA, 2007), based on practitioner logs, found 2,733,040 cephalometric images produced annually in private practices, excluding the military, federal agencies, hospitals, and academic institutions. The principal application is evaluation of growth and development, as for orthodontic treatment, and for orthognathic surgery. The equipment provides for standardized positioning of the patient together with alignment of beam, subject and image receptor. It is frequently useful for the cephalometric image to show bony anatomy of the cranial base and facial skeleton plus the softtissue outline of facial contours Fluoroscopy. Real-time imaging, or fluoroscopy, is useful only for imaging motion in structures. Its use should be limited to those tasks requiring real-time imaging, such as the injection of radiographic contrast fluids for sialography or temporomandibular joint arthrography. Fluoroscopy requires electronic image intensification and video display to minimize patient exposure; this equipment is expensive and not usually found in dental facilities. Furthermore, dental x-ray machines are not generally capable of providing the required continuous radiation exposure Recommendation 33. Fluoroscopy shall not be used for static imaging in dental radiography. If fluoroscopy is used for dynamic imaging, the practices in NCRP Report No. 168 shall be followed Cone Beam Computed Tomography. The CBCT examination is a complementary modality to, not a replacement for, two-dimensional imaging modalities. Just as for other dental radiographic examinations, justification for each patient should be based on their imaging history and the diagnostic yield not achievable with the 2D modalities. The examination is justified if the anticipated diagnostic yield outweighs the risks associated with radiation (AAOMR, 2008; ADA, 59

60 ; EADMFR, 2009; Farman and Scarfe, 2006; White and Pae, 2009). CBCT should only be used when the question for which the imaging is required cannot be answered adequately by conventional, lower dose dental radiography, applying the ALARA principle (NCRP, 2003). This is especially true for CBCT examinations of children (SPR, 2015) Prior to the acquisition of a CBCT examination, a dental examination by the ordering provider should be completed, with a review of the patient s medical history, as well as the medical and dental imaging history. Previously acquired dental and medical imaging, which falls short of yielding the necessary clinical information, may justify the need for the CBCT examination (ADA, 2012; Farman and Scarfe, 2006). The decision for the clinical indication for CBCT is the professional determination of the treating clinician. Some of the evidence-based specific indications for CBCT imaging are provided in Section Image Viewing Environment Poor viewing conditions can suppress the clinician s ability to perceive important diagnostic information that is present in the image. This may lead to diagnostic errors or unnecessary repeat examinations in an attempt to produce an improved image to compensate for the poor viewing conditions. It is essential to assure appropriate viewing conditions to insure optimal interpretation and to avoid repeating adequate images that appear substandard due to substandard viewing conditions (Kutcher et al., 2006; Patel, 2000) For maximum diagnostic yield at minimum exposure, image evaluation and interpretation is best carried out in a quiet atmosphere, free from distractions. With film radiographs, perception of image details has been shown to be maximum when the illuminated surface of the view box that is not covered with films or by the opaque film mounts is masked with opaque material to eliminate glare. View boxes are available that allow for adjusting the luminance and digital displays allow for adjusting the image brightness and contrast. These view boxes need to be maintained by periodic cleaning, visual assessment of uniformity and assessment of luminance. With digital images, perception of image detail is maximized when the illuminated areas of the display surrounding the digital image are electronically masked to reduce glare. 60

61 When viewing either film radiographs or digital images, reduced ambient (room) light is required to maximize the perception of image details. As a rule of thumb, the lighting in the reading area should be at a reduced level but with sufficient light that one can read a newspaper page Viewing Conditions for Digital Images. In addition to the general considerations covered above, the information obtained from all digital images (intraoral, panoramic, cephalometric, and CBCT) that are viewed on a computer display are subject to a number of conditions, including those of the viewing environment. Some conditions that may affect specifically the appearance of the digital display include: ambient room lighting conditions; viewing display quality, position and location, settings, calibration, and defects; reflections of light sources (i.e., overhead lights, windows); and computer graphics capabilities A discussion of optimal configurations for computer and display hardware is beyond the scope of this report. However, an aspect of image viewing that can have a substantial impact on the perceived image quality is the room environment where clinical images are viewed and assessed. While most computer displays can be configured to provide a nominal brightness under well-lit room conditions, a darkened room environment provides an improved viewing experience and higher clinical benefit. Pakkala et al. (2012) investigated the effect of ambient viewing conditions and computer display brand on sensitivity and specificity for diagnosis of caries. Based on their findings Pakkala et al. recommend that darkened ambient room conditions be employed, noting that their data suggests that simply increasing the display brightness was not a recommended alternative. The authors further note that in those practices where clinical images are routinely displayed chair-side near the patient (and presumably under room conditions providing a high level of ambient light), it is advisable to confirm diagnosis under subdued viewing conditions, as their data regarding sensitivity suggest

62 In the early days of digital imaging, images were presented on cathode ray tube (CRT) monitors which have largely been replaced by flat-panel displays. A flat panel displays is composed of a rectangular array of pixels that determine the spatial resolution of the image. Spatial distortion is not likely, because the pixels are fixed in position, and spatial resolution is not likely to vary, because the size of the pixels does not change. However, the luminance of the backlight tends to decrease with time. There are differences between commercial computer displays and medical grade displays, although some studies have shown comparable diagnostic efficacy for detecting anatomic sites and common dental pathology (Kallio-Pulkkinen et al., 2014; Tadinada et al., 2015a) Recommendation 34. Images shall be viewed in an environment adequate to ensure accurate interpretation Use of Radiation Protective Aprons Radiation protective aprons for patients were first recommended in dentistry many years ago when dental x-ray equipment was much less sophisticated and image receptors were much slower than under current standards and when the primary risks were thought to be heritable effects. They provided protection in an era of poorly collimated and unfiltered dental x-ray beams. Gonadal (or whole-body) doses from these early full-mouth examinations, reported as high as 50 mgy (Budowsky et al., 1956), could be reduced substantially by radiation protective aprons. Gonadal doses from current panoramic or full-mouth intraoral examinations using stateof-the-art technology and procedures do not exceed 5 µgy (White, 1992). A substantial portion of this gonadal dose results from internal scattered radiation arising within the patient s head and body. Technological and procedural improvements have eliminated the requirement for the radiation protective apron, provided all other recommendations of this Report are rigorously followed. However, some patients have come to expect the apron and may request that it be used. Its use remains a prudent but not essential practice

63 Recommendation 35. The use of radiation protective aprons on patients shall not be required if all other recommendations in this Report are rigorously followed unless required by state regulation Otherwise, a radiation protective apron shall be used Use of Thyroid Collars. The thyroid gland, especially in children, is among the most sensitive organs to radiation-induced tumors, both benign and malignant (Appendix I). Even with optimum techniques, the primary dental x-ray beam may still pass near and occasionally through the gland. If the x-ray beam is properly collimated to the size of the image receptor or area of clinical interest, and exposure of the gland is still unavoidable, any attempt to shield the gland would interfere with the production of a clinically-useful image. However, in those occasional uncooperative patients for whom rectangular collimation and positive beam-receptor alignment cannot be achieved for intraoral radiographs, then thyroid shielding may reduce dose to the gland without interfering with image production Recommendation 36. Thyroid shielding shall be provided for patients when it will not interfere with the examination Maintenance of Protective Aprons and Thyroid Shields. Minimum acceptable evaluation of radiation protective aprons and thyroid shields consists of periodic visual inspection for defects. Fluoroscopic evaluation of lead aprons is not recommended as this exposes the inspector to substantial scattered radiation (NCRP, 2010) Recommendation 37. Protective aprons and thyroid shields should be hung or laid flat and never folded, and manufacturer s instructions should be followed. All protective shields should be evaluated for damage (e.g., tears, folds, and cracks) quarterly using visual and manual inspection

64 Special Considerations for Pediatric Imaging Children are not small adults. Some tissues in children, including thyroid and female breast, are two to ten times more sensitive to radiation carcinogenesis than adults, due to higher levels of cell proliferation, more cells which are less differentiated, and a much longer proliferative future (Hall and Giaccia, 2011). Additionally, the thyroid gland in children is higher in the neck than in adults, thus more thyroid tissue is in the radiation field. It is imperative to child-size all radiation exposures of children commensurate with the diagnostic need of the examination Recent studies have suggested that the lens of the eye may be more susceptible to cataractogenesis than previously thought (ICRP, 2012). The use of leaded glasses has been shown to significantly reduce the dose to the lens during cone beam CT examinations (Prins et al., 2011). Thus, leaded glasses should be considered when the orbital and periorbital regions are not essential to the image (as they might be for pre-orthognathic surgical treatment planning) It is essential to assure that pediatric patients are not treated as adult patients with regard to x-ray techniques. The following guidelines should be observed when imaging pediatric patients ( select x rays for individual s needs, not merely as a routine; use the fastest image receptor possible (E- or F-speed film, or a digital receptor); collimate beam to area of interest; always use thyroid collars unless it interferes with imaging the needed anatomy; child-size the exposure time, i.e., optimize the image quality and patient radiation dose; and use cone-beam computed tomography only when clinically necessary Further information on imaging pediatric patients can be found on the Image Gently website (

65 Recommendation 38. Technique factors and selection criteria shall be appropriate to the age and size of the patient Protection of the Operator Equipment and procedures that reduce patient exposure will also reduce exposure of the operator and the environment. Additional measures, however, will further reduce occupational and public exposure without affecting patient dose or image quality Shielding Design Attention to office layout and shielding design provides convenient methods for implementing the ALARA principle. Shielding does not necessarily require lead-lined x-ray rooms. Normal building materials may be sufficient in most cases. Expert guidance can provide effective shielding design at nominal incremental cost with protection by barriers, distance from x-ray source, and operator position Recommendation 39. Adequacy of facility shielding shall be determined by the qualified expert whenever the average workload increases by a factor of two or more from the initial design criteria It is in the economic best interest of the dentist to obtain shielding design by a qualified expert at the facility design stage. For a new or remodeled facility, proper shielding design can usually provide radiation protection to meet shielding design goals at little or no incremental construction cost. However, if post-construction measurements indicate that these goals are not met, the cost of retrofitting may be considerable Barriers Fixed barriers, generally walls, provide the most economical, effective and convenient means of excluding the public and nonoperator office staff from the primary x-ray beam as it exits the 65

66 patient or from radiation scattered from the patient or other objects in the primary beam. Windows (glass, leaded glass or acrylic) in permanent barriers, mirrors, or remote video monitoring may be helpful Barriers are not necessary for protection of the operator of appropriately designed hand-held x-ray units as these have a nonremovable circular shield built into the device Recommendation 40. Shielding designs for new offices with fixed x-ray equipment installations shall provide protective barriers for the operator. The barriers shall be constructed so operators can maintain visual contact and audible communication with patients throughout the procedures Recommendation 41. The exposure switch should be mounted behind the protective barrier such that the operator must remain behind the barrier during the exposure Distance In some existing facilities, design precludes use of a protective barrier. Appropriate distance and position relative to the position of the x-ray tube and direction of the x-ray beam must be maintained in these situations Recommendation 42. In the absence of a barrier in an existing facility, the operator shall remain at least 2 m, but preferably 3 m, from the x-ray tube head during exposure. If the 2 m distance cannot be maintained, then a barrier shall be provided. This recommendation does not apply to hand-held units with integral shields Position of Operator If the facility design requires that the operator be in the room at the time of exposure, then the operator should be positioned not only at maximum distance (at least 2 m) from the tube head, and also in the direction of minimum exposure (Figure 4.1). Maximum exposure will 66

67 Fig Recommended positions for operator exposing intraoral images of the central incisors (left) and molars (right). Operator should stand at least 6 feet from the patient and an angle of 90 to 135 degrees from the central ray (Richards, 1964; White and Pharoah, 2014)

68 generally be in line with the primary beam as it exits the patient. Maximum scattered radiation will be backwards, i.e., 90 to 180 degrees from the primary beam as it enters the patient. Generally the position of minimum exposure will be at 45 degrees from the primary beam as it exits the patient, see Appendix E2 (de Haan and van Aken, 1990). In particular, the operator should not stand on the side of the patient opposite the x-ray tube as this would expose them to the direct x-ray beam exiting the patient Personal Dosimeters Monitoring of individual occupational exposures is generally required if it can be expected that any dental staff member will receive a substantial dose. Occupational Safety and Health Administration (OSHA) regulations state that individuals who are occupationally exposed to x rays and who may receive >25 % of the quarterly occupational dose limit, are required to wear a dosimeter [29 CFR (d)(2)(i)]. NCRP (1998) recommends that personal dosimeters be provided to all personnel who are likely to receive an effective dose >1 msv y 1. It must be emphasized that this recommendation concerns effective dose, which is generally much less than the dose measured by personal dosimeters. The most recent available data (Table 3.1) indicate that the average annual occupational dose in dentistry in the United States in 1980 was 0.2 msv y -1 (Kumazawa et al., 1984) and in Canada from 1970 to 1987 was msv y 1 (Zielinski et al., 2005). Few dental workers received >1 msv and 68 % received exposures below the threshold of detection World data for the period 2000 to 2002 show a mean annual occupational dose of 0.06 msv for dental workers (UNSCEAR, 2008). These data suggest that dental personnel are not expected to receive occupational exposures greater than the recommended threshold for monitoring of 1 msv y -1. However, the limit applicable to pregnant workers of 0.5 msv equivalent dose to the fetus per month once pregnancy is known suggest that personal dosimetry may be a prudent practice for pregnant workers. Current regulations require that dosimeters be obtained from services accredited for accuracy and reproducibility. These services distribute dosimeters regularly; the facility returns the dosimeters to the service after use (generally monthly or 68

69 quarterly) for readout and report. The return frequency for personal dosimeters for pregnant staff should be monthly or more frequent Recommendation 43. Provision of personal dosimeters for external exposure measurement should be considered for workers who are likely to receive an annual effective dose in excess of 1 msv. Personal dosimeters shall be provided for declared pregnant occupationally-exposed personnel Recommendation 44. For new or relocated equipment, the facilities shall provide personal dosimeters for at least 1 y in order to determine and document the doses to personnel Recommendation 45. The facility shall provide personal dosimeters for all new operators of hand-held dental x-ray equipment for the first year of use Protection of the Public For shielding design purposes, the public consists of all individuals, including nonoccupationally exposed staff, who are in uncontrolled areas such as reception rooms, other treatment rooms, or in adjacent corridors or offices in the building within or outside of the dental facility (NCRP, 2005). The popular open design dental facility, which places two or more treatment chairs in a single room, may present problems Recommendation 46. In dental facilities using large, multi-patient open bay designs, a patient in proximity to another patient being radiographed shall be treated as a member of the public for radiation protection purposes Recommendation 47. When portable or hand-held x-ray machines are used, all individuals in the area other than the patient and operator shall be protected as members of the public. 69

70 The annual limit on effective dose to a member of the general public, shielding designs should limit exposure to all individuals in uncontrolled areas to an effective dose that does not exceed 1 msv y 1 (NCRP, 2004a; 2004b) Recommendation 48. New dental facilities shall be designed such that no individual member of the public will receive an effective dose in excess of 1 msv annually

71 Quality Assurance and Quality Control Image quality must strike a balance between providing the information necessary for the diagnosis and the lowest possible radiation dose. Reducing the dose excessively at the expense of producing a nondiagnostic image is not a good practice. Conversely, exposing a patient to excessive dose to produce an esthetically pleasing image beyond that needed for diagnosis is not a good practice either. The goal is to strike the appropriate balance between a diagnostically acceptable image and the lowest possible radiation dose. Quality assurance is the planned and systematic activities necessary to provide adequate confidence that a product or service will meet the given requirements. Quality control is the routine performance of equipment function tests and tasks, the interpretation of data from the tests, and the corrective actions taken (NCRP, 2010) Image Quality and Patient Dose Optimization Image Quality Image quality that is appropriate for the specific diagnostic task is essential in dental radiography. Reduced image quality can result in missed or unobservable pathology and lead to misdiagnosis or mistreatment. However, image quality should not be maximized without regard for patient dose. Digital intraoral receptors, for example, can produce exceptional image quality at doses that well exceed optimal values. It is essential to optimize the balance between image quality and patient dose (Section 4.3). This means that image quality and patient dose go hand-in-hand, especially in digital modalities. In particular, facilities operating with median doses above the DRL should explore ways that they can reduce their doses, keeping in mind that the images must be clinically acceptable (Section 4.2). However, being below the appropriate DRL, by itself, does not imply that doses have been fully optimized The older technology of film-based imaging provided a built-in means for limiting dose: excessive exposure to the film would generally result in a film so optically dense, or dark, that it is virtually useless for diagnostic purposes. Under-development of film (low developer 71

72 temperature or improper replenishment of developer solution) will result in excessive patient doses and poor image quality (low contrast) Solid state image receptors can offer a reduction in radiation required to produce an image (Anissi and Geibel, 2014). Patient skin entrance dose per image can be reduced from ~100 µgy with F-Speed film to ~40 to 80 µgy with a solid state receptor (Table 6.1) while still producing diagnostically acceptable images. Surveys have shown, however, that many solid state receptors are using doses similar to or higher than D-speed film (Walker et al., 2014). 1 This has been primarily attributed to the dentists not changing their x-ray techniques when switching from film to digital solid state receptors. In addition, Farman and Farman (2005) have shown that practitioners are using 1.5 to 20 times the exposure necessary to produce a diagnostically useful image. This overexposure is then compensated for by the digital imaging system software, thereby providing no indication of overexposure to the user. In addition, it is advisable for the clinical practice to become familiar with the exposure response of the particular digital system they implement in order for the patient to benefit from the reduced exposures associated with digital imaging An additional problem with the use of solid state receptors is a consequence of their ease and speed of use, which make retakes easy and fast. This can result in multiple image acquisitions and total patient doses greater than when film is used (Berkhout, 2003). Therefore, it is critically important that repeat images be obtained only when absolutely needed for diagnostic purposes Give the rapidly advancing technology of image receptors, with increasing receptor speed, it is important that newly purchased x-ray machines be able to correctly expose such receptors Recommendation 49. X-ray machines should provide a range of exposure times suitable for twice the speed of the fastest available image receptors Gray, JE (2015). Personal Communication. (DIQUAD, LLC, Steger Illinois) 72

73 Patient Dose Patient doses can be controlled or optimized using many techniques. The speed of the image receptor is the most important. For example, the use of F-Speed film or digital receptors in place of D-Speed film can reduce the dose to the patient by ~50 % or more in intraoral imaging. In panoramic and cephalometric imaging, use of rare-earth screen-film combinations or digital receptors allows for substantial reduction of patient dose Film processing requires careful attention to the concentration and temperature of the solutions and the time the films spends in each solution. Improper processing can render a properly exposed image nondiagnostic and useless. It can also lead to an increase in patient radiation dose as the developer solution is depleted the x ray exposure time must be increased to obtain appropriate film density In addition to receptor speed, use of rectangular collimation in intraoral imaging reduces the effective dose to the patient by an additional 80 % (Ludlow, 2008). As an added bonus, rectangular collimation reduces scatter and improves image quality In CBCT imaging, a variety of factors are available to reduce patient dose, including field-ofview, milliampere-seconds, voxel size, and spatial resolution, 360 versus 180 degree movement, and avoiding the use of machine exam presets such as high definition (HD) only when necessary. These must be selected judiciously with diagnostic objective and patient dose in mind Technique Charts Regardless of image receptor speed, another method to insure image quality, while reducing patient dose, is the utilization of size-based technique charts. Technique charts should be developed for each x-ray unit and image receptor combination. These should include technique settings for specific anatomical areas in combination with the patient size (small, medium, large) for adults and children. These should be developed for both intraoral and extraoral imaging, listing the exam, patient size, along with adult and pediatric settings, and image receptor (film 73

74 type, digital image receptor). It is not adequate to use equipment manufacturer technique charts without validation. Technique charts should be posted conveniently near the control panel where the technique is adjusted for each x-ray unit. With digital workstations, technique charts may also be readily placed on the workstation s desktop. When the x-ray unit is replaced, or an image receptor is added, the chart must be updated (see Section for further information on technique charts) Quality Control Quality control (QC) is an integral component of a quality assurance (QA) program. As noted above QA is the overall program for assuring quality outcomes. QC, on the other hand, is the part of the QA program that employs regular physical testing designed to detect changes in a radiographic system before they can interfere with diagnostic performance. Lack of a quality control program often results in poor quality images, lacking clinically necessary details for diagnostic purposes, increasing radiation doses to the patient and staff, and repeated images resulting in increased radiation dose The QC program for each facility must be customized to the imaging modalities in use, the staffing capabilities and equipment available. The QC program should be established in consultation with the qualified expert, documenting specific QC activities, the personnel responsible for performing each activity (e.g., dental assistant, qualified expert), procedures to be followed for each activity, acceptable ranges of results, and actions to be taken when results of any QC activity are not within the acceptable range. Such a program includes daily, weekly, monthly, quarterly, and annual tests of the various components of the imaging chain. In general, QC activities that should be performed frequently do not entail complex equipment or procedures and can be performed by on-site dental assistants or other technical staff. More complex tasks or those requiring specialized training or equipment should be performed by the qualified expert at intervals consistent with the probability of undetected failure, the impact of failure on patient care, and the availability of the qualified expert

75 All dental facilities utilizing x-ray imaging should be evaluated initially (acceptance testing, also known as initial equipment performance evaluation) and periodically thereafter by a qualified expert. This will assure that the image quality and the patient radiation dose are appropriate, persons in the vicinity of the x-ray equipment are safe, regulatory compliance is maintained, and that the facility staff is maintaining their portion of the quality control program No matter what image receptor is used, the QC program should include periodic testing and calibration of the x-ray system in order to see that tube-head stability, collimation, tube potential, half-value layer, exposure time, output reproducibility, and other factors are within the appropriate tolerances. Once it is ascertained that the x-ray unit is functioning properly, the image receptor can be evaluated using this calibrated x-ray unit for test exposures Radiation Measurements of X-Ray Producing Diagnostic Dental Equipment The qualified expert is the individual who is responsible for, and qualified to measure radiation dose, interpret the results, and advise on the clinical implications of dose and image quality in imaging facilities, including dental facilities. While measuring radiation dose may appear a simple task, the qualified expert must be familiar with many complex technical factors when measuring and evaluating dose in dental facilities. Different types of radiation detectors are suited to different types of radiation measurements, and different units of measure are used for different modalities. For example, a radiation detector that is suitable for measuring entrance skin exposure in dental radiography may or may not be suitable for measuring dose in a CBCT system, depending on the units used and the comparisons to be made. Measurements of exposure to persons in the vicinity of an x-ray producing device must be made with an entirely different type of radiation detector. Both types of radiation measurement are required for regulatory compliance in many jurisdictions When changing from film to digital imaging, the settings used for film will typically deliver unnecessarily high radiation to the patient, often by a factor of two or more. Hence, the qualified expert should be consulted before converting to digital image receptors, so that the exposure factors may be reduced before commencing patient imaging. The manufacturer may provide 75

76 suggestions for technique factors, but only the qualified expert has the knowledge and equipment needed to accurately measure radiation dose, interpret those data, and to advise the dental practitioner about the appropriate technique factors to be used with a new digital receptor While service engineers can perform radiation measurements in dental imaging facilities, their results do not replace the testing by a qualified expert Phantoms for Quality Control and Dose Measurements There are a limited number of imaging phantoms that are designed specifically for dental imaging. When these are not readily available, the qualified expert may adapt conventional radiography phantoms that are appropriate to the field size and image quality considerations relevant to dental radiography The FDA requires that phantoms be provided by the CBCT manufacturer to assess specified image quality indicators. Conventional head CT phantoms for image quality and dose measurements (CTDI) may be used if considered appropriate by the qualified expert. Dose measurements may also be made in air, without the use of a phantom. Some equipment manufacturers may provide tabulation of dose-area product for equipment capable of CT-like imaging Recommendation 50. A suitable radiographic phantom shall be used to optimize radiation dose and image quality, and for continuing quality control measurements Quality Control for Film Imaging For facilities using film-based radiography, the greatest single source of image variability is film processing. The facility QC program should follow the film processor manufacturer s recommendations for quality control. The most critical element of film processing quality control (whether hand developing or using an automatic film processor) is to assure that the processing 76

77 chemistry is maintained at the specified temperature (appropriate for the processing time), remains fresh (i.e., undiluted and uncontaminated), is replenished daily, and replaced regularly Film processing solutions are subject to gradual deterioration. The deterioration may go unnoticed until it becomes severe enough to degrade image quality and require an increase in exposure time, thus increasing patient dose. Daily measurements are required to prevent this degradation A baseline radiographic image is first produced using fresh solutions at proper temperatures. A standardized test object [step wedges are commercially available or can be assembled from discarded lead foil from film packets (Valachovic et al., 1981; White and Pharoah, 2014)] is placed on the film, exposed, and processed to produce this baseline image. Subsequent images are produced daily under identical conditions. The follow-up images are compared to the baseline images and corrective actions are taken if changes in the image quality are noted. The images are saved for later reference, and records are maintained of any image technical factors that are measured and any changes or repairs that are made Film processing quality control is essential to maintaining optimum quality radiographic images and assuring patient doses are as low as reasonably achievable. This is required by some state radiation protection agencies Whether using manual- or automatic-film processing, the specified development time and temperature must be used. If manually processing films, the films must be agitated during processing according to the film manufacturer s instructions Developer and fixer solutions must be replenished with eight ounces of appropriate solutions each day before processing patient films (solutions must be stirred to assure the new solutions are mixed thoroughly with the older solutions). All solutions should be drained, the tanks cleaned, and refilled with fresh solutions at least every two weeks

78 The water in the wash tank should be changed daily or after every 30 intraoral films that are processed, whichever occurs first. For higher volumes or larger films, such as panoramic or cephalometric, the water should be changed more frequently Recommendation 51. Film processing quality shall be evaluated daily, before processing patient films, for each film processor or manual processing system Quality control for film processing is an essential part of assuring optimum film quality while minimizing radiation dose to the patients and staff. The tests and tasks (Table 5.1) are easy to carry out and take very little time Quality Control for Digital Imaging Receptors It is important to make sure that the quality of the digital images produced with any type of image receptor is adequate for diagnostic purposes. Often the quality of the images from the image receptors or storage phosphor plates are evaluated subjectively, thereby leading to the possibility that there is no consistency in determining when a storage phosphor plate should be replaced, when a digital image receptor has been damaged, or the image quality has deteriorated. Studies have shown that objective evaluation of some critical parameters such as spatial resolution, contrast detail detectability, and dose-response curve over a wide range of exposures can be used to confirm the quality of the images made from storage phosphor plates or traditional digital image receptors. A typical QC phantom for dental digital imaging systems is shown in Figure While there is no clear standard on how often image quality must be tested on different digital imaging systems it is recommended to test after 40 exposures on storage phosphor plates and once every three months for digital image receptors using a phantom which is capable of testing critical characteristics like spatial resolution, contrast, freedom from artifacts and dead pixels, and dose response over a wide range of exposures

79 TABLE 5.1 Frequency of quality control testing for film-based radiography. a QC Task Frequency Who Darkroom fog At least annually and when fog is suspected Office staff Developer and fixer replenished with solution recommended by manufacturer Daily Office staff Change developer and fixer solutions Every two weeks or more frequently for a busy practice Office staff Developer, fixer, wash temperature Check daily before processing films Office staff Change water in wash tank Daily If more than 30 films per day, then after every 30 films Office staff X-ray machine performance Not to exceed every 4 y. Annually is ideal Qualified expert a For more detail, the reader is referred to Appendix A

80 Fig A phantom for measuring image quality in intraoral digital radiography, constructed of tissue-equivalent Lucite with test objects imbedded internally. When the position-indicating device is placed on the four plastic rest tabs as shown, the geometry of intraoral digital radiography is simulated

81 There are a few activities that can assist in maintaining a quality digital imaging system. For PSP-based devices, these include cleaning the sensor plate surface and the transport assembly regularly and when artifacts are observed (using only cleaners recommended by the manufacturer), and replacing the plates when they become damaged or stained. For many technical problems the only course of action is a service visit. Some manufacturers also recommend that certain mechanical parts within the scanner be replaced every 2 to 4 y. Although not an aspect of routine quality control, a means for ensuring that the PSP plates are exposed on the correct side is recommended, given the ease with which a PSP image receptor may accidentally be exposed on the opposite side, leading to the potential for incorrect viewing and clinical evaluation. Another issue with PSP plates is the propensity for scratching and fraying of the edges during handling. Damaged plates must be replaced in order to maintain quality imaging A quality control program can reduce patient dose while optimizing diagnostic quality images. Figure 5.2, which comes from a study examining implementation of a digital QC program in private dental offices, demonstrates this well Quality Control for CBCT Facilities utilizing CBCT imaging should follow the imaging equipment manufacturer s specific instructions for quality control. CBCT manufacturers are required by the Federal Performance Standard [21 CFR (c)(3)(d)] to provide a CBCT QC manual and appropriate phantom that evaluates specified elements of image quality. If a CBCT system has been installed without such a quality assurance manual and phantom, the dental practitioner or administrator should contact the CBCT manufacturer to obtain the required QC manual and phantom. Both the QC manual and phantom are essential elements of the QC program. A typical QC phantom for dental CBCT systems is shown in Figure 5.3 (some phantoms are available with software to analyze the CBCT QC images)

82 Fig Distribution of skin exposures before and after quality control (adapted from Walker et al., 2014). The average skin exposure is substantially reduced after a quality control program is implemented For further detail, the reader is referred to Appendix B

83 Fig A typical dental CBCT phantom for quality measurements, constructed of tissueequivalent plastic or similar material, and with imaging test objects embedded internally. It is placed in the machine where the patient s head would be and then exposed to measure the various characteristics of the acquired volume

84 Quality Control for Image Displays Since digital radiographs are viewed on a computer display, the display must be calibrated and evaluated. Digital radiographs should be viewed with the center of the display positioned slightly below eye level. Subdued lighting should be used and every effort should be made to eliminate glare and reflections from extraneous sources of light such as room lights, view boxes, and windows It is essential that the computer display used to view digital dental images be properly calibrated in terms of brightness and contrast. The Society of Motion Picture and Television Engineers (SMPTE) test pattern (Figure 5.4) is almost universally available in the medical imaging community for this purpose. This pattern should be available on the digital imaging system, i.e., stored on the computer hard drive. If not, the vendor or manufacturer should be able to provide a copy. It is also readily available on the internet The brightness and contrast controls are adjusted to obtain a display image similar to those in Figures 5.2. Of particular importance are the 0 % and 95 % patches which are inset in the 5 % and 100 % squares of the test pattern. Both of these should be visible when the window width is set to encompass the maximum pixel range for the computer system, usually 0 to The SMPTE pattern also provides high contrast (black and white) and low contrast resolution patterns in the center and four corners. The mid-gray cross hatch pattern can be used to measure distortion of the display from image processing software and for older cathode ray tube (CRT) displays Quality Control Tests and Frequency for Digital Radiography Quality control tests must be carried out regularly and the results documented. Most of these tests (Table 5.2) take very little time but assure the quality of the digital radiographic images

85 Fig Society of Motion Picture and Television Engineers (SMPTE) test pattern provides a standard image for calibration and evaluation of computer displays. Left arrow 0 % patch in 5 % square; right arrow 95 % patch in 100 % square (Gray, 1985)

86 1949 TABLE 5.2 Frequency of quality control tests for digital radiography. QC Task Frequency Who X-ray machine performance: Intraoral, panoramic, cephalometric Not to exceed every 4 y. Annually is ideal. Qualified expert X-ray machine performance: CBCT Every 1 2 y Qualified expert Display Performance Quarterly Staff (using SMPTE Test Pattern) Evaluate images from PSP plates for artifacts Visually inspect CR plates with each use Evaluate each image for artifacts Staff Evaluate digital sensor images for artifacts Evaluate each image for artifacts Staff Evaluate junction between cable and sensor Daily Staff Phantom test PSP plate performance Every 40 exposures per plate Staff Phantom test CCD or CMOS sensor Quarterly for each sensor Staff

87 Infection Control Dental radiologic procedures are conducted using universal precautions that prevent transfer of infectious agents among patients, operator, and office staff. All equipment and procedures should be compatible with current infection control philosophy and techniques, while still maintaining the ALARA principles. It is important that a rigorous, written infection control policy be developed and routinely applied. These practices apply especially to intraoral radiography, in which multiple projections are commonly used in a single examination. The image receptors are placed in a contaminated environment. Gloved hands of the operator who is observing universal precautions can become contaminated when placing image receptors in the mouth or removing exposed ones from the mouth. This contamination then can be easily spread, such as to the x-ray machine and to image processing equipment. Universal precautions are mandated by the Occupational Safety and Health Administration to prevent dissemination of contamination (OSHA, 2015). Details for dental imaging infection control procedures can be found in most oral and maxillofacial radiology textbooks (White and Pharoah, 2014) Recommendation 52. There shall be an infection control policy to protect staff and patients that encompasses imaging equipment and procedures Recommendation 53. Imaging equipment and devices should be designed to facilitate standard infection control precautions

88 Image Receptors Direct Exposure X-Ray Film General Information Patient doses for intraoral film radiography have decreased dramatically since 1920 (Figure 6.1). In fact, the doses today are ~1 % of that used in the early twentieth century (Richards and Colquitt, 1981) Since the mid-1950s the most common image receptors for intraoral radiography in the United States has been direct exposure film of American National Standards Institute (ANSI) Speed Group D (Goren et al., 1989; Platin et al., 1998). Faster films, ANSI Speed Group E, were introduced in the early 1980s, with improved versions coming in the mid-1990s. These faster films have been widely used in Europe (Svenson and Petersson, 1995; Svenson et al., 1996). Published data show that these faster films provide for patient and staff dose reductions of up to 50 %. However, early E-speed films exhibited decreased contrast and higher sensitivity to processing conditions than were found with D-speed films (Diehl et al., 1986; Thunthy and Weinberg, 1982). These problems have been corrected and presently E-speed film can be used with no degradation of diagnostic information (Conover et al., 1995; Hintze et al., 1994; 1996; Kitagawa et al., 1995; Ludlow et al., 1997; Nakfoor and Brooks, 1992; Price, 1995; Svenson et al., 1997a; Tamburus and Lavrador, 1997; Tjelmeland et al., 1998). Digital image receptors with speeds similar to or faster than E-speed film are available. Intraoral films of speed group F are commercially available, perform at the same diagnostic levels as both D- and E-speed films and are suitable for routine use (Farman and Farman, 2000; Ludlow et al., 2001; Thunthy, 2000). (One manufacturer produces an E-F-speed film. It is E-speed when hand processed and F-speed when machine processed.) In spite of the fact that use of E and F speed film was a shall statement in NCRP Report No. 145 (NCRP, 2004), the most recent study of the relative use of D and F speed films in the United States showed that 78 % of film users continue to use D-speed film (NEXT, 2015). In fact, D-speed film requires the same exposure to the patient as it did in

89 Fig Approximate relative exposures at skin entry for intraoral radiographs, 1920 to Arrows indicate introduction of faster films (ANSI speed groups A, B, C, D, E and F, as indicated). The solid line represents smoothed best fit to the data points, illustrating the exponential downward trend of exposures over time. The exposure required for F-speed film is ~1 % of that required for the first dental films, and 50 % of that required for D-speed film (Farman and Farman, 2000). 89

90 (red circle, Figure 6.1). Studies in the United Kingdom show that only a very small minority of facilities using film for intraoral imaging use D-speed film (Holroyd, 2013) Film users are urged to update their techniques and technique charts as they adopt faster image receptors. It is incumbent on manufacturers to assist users in establishing new techniques Recommendation 54. Image receptors of speeds slower than ANSI Speed Group E-F film shall not be used for intraoral radiography, i.e., D-speed film shall not be used Equipment and Facilities After exposure, radiographic film must be processed to produce a diagnostic image. The equipment and facilities which are needed to process intraoral films must be optimized in order to generate the diagnostic image. A perfectly placed and exposed film can easily be rendered nondiagnostic by poor processing Darkroom. Each darkroom should be evaluated for light leaks and safelight performance. A coin test is performed by placing an unexposed, unwrapped intraoral film at a normal working position and putting a coin upon it. After 2 min, the film is processed. An image of the coin indicates a problem with either light leaks or the safelight. Repeating the procedure with the safelights off will determine if the fog is due to the safelights or light from outside the darkroom. These tests are should be performed at least quarterly, and preferably monthly (White and Pharoah, 2014) or following a change in the safelight filter or bulb, or other changes to the darkroom that could affect its integrity. Direct exposure films have different spectral sensitivities from those used with screens; a safelight filter appropriate for one may not be adequate for the other. In addition, the film used with screens must be pre-exposed in the cassette to produce a uniform, mid-gray density when processed in order to carry out this test Daylight loaders are commonly used with automatic dental film processors, eliminating the need for the darkroom. These systems provide light-tight boxes attached to the processor. Each box contains a port for placing exposed films (still in their wrappers or cassettes) in the box, 90

91 ports for inserting the hands so the operator may manipulate films in the box, and a viewing port through a filter similar to the safelight filter. The processor safelight filter is designed for use in a room with low-level illumination. It may be necessary to use daylight loaders only in rooms with reduced illumination. Furthermore, the daylight loader may present difficulties in infection control with intraoral film wrappers contaminated with oral fluids. Like the darkroom, the daylight loader may be evaluated for light leaks using the coin test (AAPM, 2015) Recommendation 55. Each darkroom and daylight loader shall be evaluated for fog at initial installation, and then at least quarterly and following change of room lighting or darkroom safelight lamp or filter Storage of Radiographic Film. It is essential to protect radiographic film in storage from radiation exposure. Radiographic film used in film-screen imaging is less sensitive to direct radiation exposure today than in the past (Suleiman et al., 1995) Recommendation 56. Film, including film in cassettes, shall not be exposed to excessive radiation during the period it is in storage Film Processors. Film processing is a sequence of chemical reactions that are time and temperature dependent. Processing solutions must be at the proper concentrations. Solutions that are either dilute, excessively concentrated, or contaminated will degrade the image quality. Even with proper solution concentrations and temperatures, film processing depends on a proper combination of time and temperature. Deviations from proper processing will result in films that are of reduced contrast, and are either too light or too dark. In addition, poor processing quality commonly will result in higher radiation doses to the patient as the exposure time will be increased to obtain a film dark enough to view Recommendation 57. Film shall be processed with active, properly replenished chemicals, and time-temperature control, according to manufacturers recommendations

92 Screen-Film Systems General Information Extraoral exposures, such as for panoramic and cephalometric radiography, utilize light- sensitive film in combination with intensifying screens within a cassette. The film sensitivity must be spectrally matched to the spectrum of light emitted from the intensifying screens The intensifying screens consist of thin layers of phosphor crystals that fluoresce when exposed to x rays. The film is exposed by light emitted by the intensifying screens. Absorption of light emitted from the intensifying screens is increased by the addition of dyes to the film emulsion. The spectrum of light most readily absorbed by the film must be matched to the spectrum of light emitted by the intensifying screens Screen-film systems are widely available with varying speed, contrast, and latitude characteristics, depending on specific imaging needs. Screen-film combinations are more sensitive to x rays than direct exposure x-ray film, thus reducing the level of exposure to the patient. Image sharpness, however, is decreased as a result of diffusion of light emitted from the intensifying screens to expose the film Rare-earth intensifying screens, used in conjunction with properly matched film, are the fastest screen-film combinations available. Rare-earth screens that emit green or blue light are more efficient at absorbing radiation that exits the patient and converting x-ray energy to light energy than the blue-emitting calcium tungstate screens. Patient exposure in panoramic and cephalometric radiography may be reduced by ~50 % using fast rare-earth versus slower calcium tungstate screen-film combinations with no significant difference in perceived diagnostic quality (Gratt et al., 1984; Kaugars and Fatouros, 1982). Use of screen-film systems with flat grain technology results in increased film speed without a loss of image sharpness. Rare-earth imaging systems using this film have been shown to be 1.3 times faster than a comparable system using conventional film emulsion technology without compromising diagnostic quality (D Ambrosio et al., 1986; Thunthy and Weinberg, 1986; White and Pharaoh, 2014). 92

93 Equipment and Facilities Equipment and facilities for screen-film systems are the same as for direct exposure film (Section 6.1.2) Care of Screen-Film Systems for Film-Based Cephalometric and Film-Based Panoramic Imaging. Both cassettes and screens may acquire defects during normal use. Integrity of cassettes is determined by visual inspection and by processing of an unexposed film that has been in the cassette for at least 1 h while the cassette is exposed to normal room illumination. Light leaks from the cassette will appear as dark areas or streaks on the film. Screens are evaluated visually for surface defects such as scratches or fingerprints. Screens should be cleaned periodically, following the manufacturer s instructions Poor screen-film contact leads to unsharpness in images. Screen-film contact and uniformity of response are best evaluated by exposing a film (in its cassette) overlaid with a piece of copper test screen. Visual inspection of the processed film for sharpness and uniformity of the image can assess performance of the imaging system. Unsharp areas will appear as darker areas on the image. This is a test the qualified expert can carry out during the periodic evaluation Screen-Film Speed Recommendations. It is important to use the fastest possible screen- film combination that provides the necessary diagnostic information when acquiring panoramic and cephalometric images Recommendation 58. Screen-film systems of speeds slower than ANSI 400 shall not be used for panoramic or cephalometric imaging. Rare-earth systems shall be used

94 Digital Imaging Systems General Information Digital radiography involves the acquisition of a digital image consisting of a twodimensional array of pixels. In direct digital radiography, the latent image is directly recorded by a suitable sensor. Receptors used in direct digital radiography are photostimulable storage phosphor plates (PSP) or solid state electronic devices containing either charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS) technology. At times it is necessary to convert a film image into a digital image this is referred to as indirect digital radiography. The resultant electronic image may be presented on a computer display, converted to a hard copy image, or transmitted electronically. For a historical overview of digital imaging in dentistry see Appendix C Proportion of Digital versus Film, Proportion of PSP versus CMOS-CCD. Preliminary analysis of the data from the 2015 NEXT Dental Survey shows 87 % of the sites surveyed used digital acquisitions (70 % sensors; 19 % PSP) for intraoral imaging versus 11 % for film. Of those sites using film, 78 % used D-Speed film and 22 % used F-Speed film. Only 1.2 % of all sites surveyed used rectangular collimation Advantages of Digital Imaging Compared to Film Imaging. There are numerous recognized advantages that digital-based imaging provides over film. Many of the advantages are very similar to those observed in general radiology such as the elimination of darkroom film processing, the ability to digitally manipulate images, and the ability to easily store and transmit copies of patient images. There are also advantages specific to dental radiography Recent improvements in the quality of images provided by digital-based image receptors for dental radiography have permitted the capture of dental x-ray images that provide comparable clinical value as that for film (Alkurt et al., 2007). From an image quality standpoint the benefits of digital imaging are numerous. Farman and Farman (2005) published a study of the imaging characteristics for a number of digital x-ray technologies for dentistry. Their results show a broad 94

95 range of values for spatial resolution over wide exposure ranges. The majority of systems (some with more than one configuration) have spatial resolutions >10 cycles per millimeter (c mm 1 ). Huda (2010) reported that the human can resolve ~5 c mm 1 at 25 cm, and ~30 c mm 1 at close inspection. Therefore while film still retains a lead regarding spatial resolution (~20 c mm 1 ), the visualization of clinically relevant image detail using digital technology is likely now comparable to that for film under typical viewing conditions Digital images can be modified by a variety of image processing techniques ranging from simple enlargement of the image to manipulations of image characteristics such as contrast, sharpness and ransom noise The practice of x-ray imaging should include the optimization of equipment and procedures to minimize radiation dose to the patient while providing image quality that accomplishes the clinical task. Digital image receptors can provide acceptable images at patient exposures well below those for film (Section 5.1) The following summarizes the advantages of digital imaging in dental radiography compared with film-based imaging: acceptable image quality at reduced patient x-ray dose; post processing image manipulation including contrast, density, and edge sharpness; the ability to make measurements from the image; 3D reconstruction from CBCT acquisitions; elimination of the darkroom and film processing; reduction in time spent making radiographs; space-efficient storage; teleradiology; and environmentally friendly, chemical-free imaging Potential for Dose Reductions for PSP and DR Compared with Film. Like any x-ray- based imaging modality, the clinical benefits of the modality must be weighed against the 95

96 associated risks. The x-ray system should be optimized to provide the required clinical benefit at the lowest possible radiation dose. Film used for dental intraoral radiography is directly exposed by the x-ray beam. Consequently, this direct film exposure results in a tenfold or greater radiation dose to the patient compared with screen-film combinations as used in panoramic and cephalometric imaging Dental film manufacturers have provided film types of several speed classes with differing image quality and dosimetric properties. A NEXT survey of dental facilities in 1999 found median patient entrance air kerma for routine bitewing films to be 1.6 mgy (maximum of 5.5 mgy) for D-speed class film, and 1.2 mgy (maximum of 2.9 mgy) for E-speed class film (Moyal, 2007). Direct digital and PSP-based image receptors can provide useful clinical images at substantially lower entrance doses (Table 6.1) Farman and Farman (2005), documented the ability of most tested, commercially available digital systems to provide images of acceptable image quality at lower entrance air kerma and a greater exposure latitude compared to film. This improved x-ray efficiency and the ability to digitally enhance images can allow images that might be otherwise considered to be underexposed to still provide clinical value With digital imaging systems, there is a significant potential for dose reduction compared with film-based imaging. Corresponding to the decrease in exposure time, the patient dose for PSP systems is reduced to approximately one-half or less compared to film. The main issues in digital technology are positioning errors. The size and rigidity of the image receptors, especially CCD sensors, can make them uncomfortable for the patient and difficult to accurately position compared with film packets. Combined with the ease of repeating an image, this can lead to many additional exposures and a concomitant increase in the total radiation dose to the patient, despite the reduced radiation dose per image

97 TABLE 6.1 Typical dental bitewing skin entrance dose ranges. D-speed Film Detector Type Suggested Skin Entrance Dose Ranges (mgy) a E-F or F-speed Film a Digital-PSP b Digital- CMOS b Digital- CCD b a Gray, J.E. (2015). Personal communication (DIQUAD, LLC, Steger, Illinois) b Based on 25th and 75th percentile of optimal exposure from Table II from Udupa et al. (2013). Note Required exposure for optimal image quality varies with digital image receptor type. Table 6.1 should be considered as a starting point for image quality and dose optimization

98 Patient radiation doses for intraoral images receptors can vary widely based on several factors. Table 6.1 provides suggested exposure ranges for various detectors. It should be emphasized that the image quality and patient dose must be optimized with any detector and that the exposure ranges in Table 6.1 are merely a starting point Disadvantages and Challenges of Digital Imaging. In contrast to the advantages outlined above, digital imaging also has some disadvantages Presently, most digital image receptors tend to result in some discomfort for the patient. While patients will usually agree that no imaging device is comfortable, the flexibility of film packets compared to the rigid construction of most digital image receptors gives film the advantage with regard to patient comfort. Many sensors now come in a variety of sizes to accommodate different size patients. Digital image receptor manufacturers are addressing this issue with image receptors designed for improved patient comfort. Ergonomic ease is not limited to patient considerations. Some operators find the new digital imaging receptors challenging to handle during the x-ray examination (Annisi and Geibel, 2014). PSP digital systems offer flexible image receptors providing a level of patient comfort similar to film. These systems include a digital image processing stage prior to viewing the final radiograph. The clinical challenges of examining a patient with digital-based technology will likely improve in part as educational institutions better prepare dental students for these new technologies, and as technologies continue to evolve in response to these types of issues. Collectively, these should lead to a reduction in the number of repeat images Digital dental imaging equipment makes it difficult to see the relationship between x-ray exposure and overall image quality that is readily evident when using film. The relative broad exposure latitude provided by digital image receptors, especially PSP plates with their unique linear detector latitude (Farman and Farman, 2005), and the lack of feedback that film provided regarding over- and under-exposure can lead to patient exposures that are not optimized. Far from simple, plug-n-play, digital imaging systems require proper set-up at installation as well as continuous monitoring, much like conventional film-based systems. Failure to properly install 98

99 and optimize these systems can lead to lower quality images and higher patient exposure, potentially higher than that required for D-speed film Recommendation 59. The dental practice should enlist the assistance from a qualified expert to ensure each new digital system is properly configured with regard to both patient dose and image quality The ease with which digital images can be captured and displayed, particularly for all to see, could motivate dental practices to acquire more images per patient than normally would be taken with film. Annisi and Geibel (2014), and Berkhout (2003) found that there was a slight but notable increase in the rate of images acquired per patient, particularly for CCD-based devices. This was mainly due to the receptor size and positioning of the image receptor. Therefore the dental practice should implement and adhere to imaging practices that minimize x-ray dose to patients to levels needed for the clinical task Regardless of the technology used to image patients, the dental practice should ensure the safe and secure storage of patient records including imaging exams. Unlike hardcopy film, digital images are merely data bits on a computer. Therefore a challenge to the digital-based dental office is to establish a routine practice for ensuring secure, long-term electronic storage of patient digital imaging data. This avoids unnecessary radiation resulting from duplicate examinations to replace images lost due to computer failure. Routine duplicate backup of patient images, stored off site, is a highly recommended practice to guard against unanticipated computer storage failure. Finally, the vulnerability of electronic records (medical or otherwise) to computer hacking mandates the implementation of secure equipment and records-keeping procedures to minimize this possibility In summary, the disadvantages of digital dental imaging include: high initial cost; image receptor dimensions and rigidity can cause patient discomfort ; difficulty in maintaining infection control; 99

100 maintaining secure electronic storage of patient records; ease of repeated images can motivate unnecessary retakes, resulting in increased patient radiation doses; and difficulty in identifying excessive doses, especially in the case of PSP, because unnecessarily high-dose images tend to be clinically acceptable Equipment and Facilities Digital imaging in dentistry requires specific equipment and facilities. These include the following major components: image receptors (PSP or solid-state sensor); image processor for PSP; computer systems; image display monitors; and technique charts PSP Plates. The migration to digital imaging can eliminate certain routine costs such as the purchase of film and processing chemicals. However, PSP-based image receptors have a limited lifetime of useful performance and must be periodically replaced. A limited study by Ergün et al. (2009) on a sample of PSP image receptors showed that the devices can provide clinically acceptable images over a lifetime of up to 200 exposures. However, the useful life depends on the appropriate handling of the PSP plates. Figure 6.2 shows and example of a good quality image, while Figure 6.3 shows some examples of plates that should be replaced as soon as possible. The cost of replacing PSP plates is in the range of $25 to $30 per plate. However, producing a quality image should be the priority over the cost of replacement plates. 100

101 Fig Example of good quality image of test phantom. This phantom consists of a Luxel dosimeter with an extra filter added. It is placed ~5 cm above the film or digital detector

102 Fig Examples of damaged PSP plates. (Top left) Scratches and frayed edges; (top right) Scratches or cracked phosphor; (bottom left) Scratches, stains, and low contrast; (bottom right) Stains of phosphor plate (coffee, soda?)

103 Photostimulable storage phosphor (PSP) image receptors function similar to conventional computed radiography (CR) devices in medicine. The receptor consists of a thin imaging plate encapsulated in a protective, light-proof cover. The receptor is pliable, and, therefore, provides the patient with a similar experience as with traditional film. Once the x-ray exposure is made, the plate is read. In this reading process the plate is scanned with a laser and light is emitted in proportion to the x-ray exposure of the receptor surface, with the amount of light being converted into pixel intensity values. This image is then stored as a digital image and presented on a computer display. Unlike direct digital-based technologies where the image is available nearinstantly, PSP-based imaging requires a scanning stage before the image can be viewed. Early PSP devices were capable of spatial resolution of ~6 c mm 1, compared to ~20 c mm 1 for film when exposed and processed properly. One study also found that the latent image on the PSP plate will degrade if the plate is not processed soon after the exam. Newer PSP-based systems are capable of resolutions of ~11 c mm 1 or better. Interestingly, even early PSP devices were shown to have better low-contrast performance than film (Figure 6.4) and to have better exposure latitude than CMOS based systems (Farman and Farman, 2005) and film (White and Pharoah, 2014) There are a number of benefits to PSP-based imaging for dental applications, particularly for intraoral imaging. The PSP plates are very similar in size and flexibility to film packets and do not require wires, providing patients an experience similar to film. Although a PSP image reader is required, the image plates are much less costly to replace than the direct digital image receptors, and the need for chemicals and film handling facilities (e.g., darkroom) are eliminated, although a PSP plate scanner and a low light level room are needed for handling the PSP plates. Sizes of PSP plates available for routine imaging include Size 0 (~35 22 mm) up to Size 4 (~76 57 mm). Sizes suitable for cephalometric, panoramic, and temporomandibular joint (TMJ) imaging are also available

104 Fig Images of a test phantom showing differences in contrast between a digital image (left) and film image (right). Smaller inset darker gray area in circle (upper right) is a low contrast area which is visible in the digital image but not visible in the film image. Likewise, light gray linear structures are visible on the left and barely visible on the right

105 Solid State Receptors. Unlike PSP-based imaging technology where the latent image is digitized during the storage plate readout process, the direct digital image receptors for dental radiography are digitized immediately after exposure within the image receptor, and images are available almost immediately after the exposure is made. The active receptor layer in direct digital image receptors are CMOS-based (complementary metal oxide semi-conductor) or CCDbased (charge-coupled device). Early receptor devices provided only a wired connection for data transfer to a computer for processing and eventual display. Newer systems are now capable of wireless transmission of image data. Direct digital image receptors are rigid; therefore patients may not tolerate them as readily as they might with conventional film packets or PSP image receptors. Aside from some potential patient discomfort, a benefit from direct digital imaging is the near-instant availability of clinical images. Similar to PSP-based systems, direct digital-based image capture provides all the benefits of electronic image processing and display, archiving, and communications of images There are a number of benefits to CCD- and CMOS-based imaging for dental applications. In comparison to film, solid state digital receptors have a much wider dynamic range and are partially decoupled from the characteristics of the entering x-ray beam. Software applications allow manipulation of the displayed image to rescue nondiagnostic raw images, thus avoiding reexposure of the patient. An underexposed receptor image can be manipulated to improve contrast and density; however, such manipulation will lose fine detail. Conversely, an overexposed receptor image will yield useful information with post-processing, at the expense of unnecessarily overexposing the patient (in this case, post-processing is comparable to the overexposure and underdevelopment of film) Solid state detectors are subject to damage and other issues associated with electronic imaging. Some examples detectors that should be replaced are shown in Figure

106 Fig Examples of solid state detectors with problems degrading image quality. (Top left) honey-combed background can be eliminated by appropriate subtraction of flat-field image. This detector also shows a chip on left, a line across the detector, and a light, cone-shaped area. (Top right) residual latent image from a high density object (step wedge) due to failure to erase or clear the sensor image before acquiring the next image. (Bottom left) background pattern of unknown origin. (Bottom right) pattern caused by short in the cord connecting the detector to the computer (courtesy of W.D. McDavid and J.E. Gray)

107 Converting from Film to Digital Imaging Potential Dose Reduction. Digital radiography offers advantages to the dentist and ancillary staff. The image is available almost instantly; there is no need for a darkroom or film processing; images can be stored and retrieved digitally; and radiation dose reductions on the order of 40 to 70 %, or more, are possible compared to film radiography (Table 6.1). However, the ease and speed of acquisition and viewing can lead to unnecessary re-exposures. In addition, post-processing image manipulation can lead to inappropriate radiation doses to patients and less than ideal, or even nondiagnostic, images; this is especially true with PSP plates where inadvertent overexposure is easily done. These two practice behaviors can lead to systematic overexposures to the patients Recommendation 60. When converting from film to digital imaging, the facility shall make proper exposure technique (time) adjustments, commensurate with the digital imaging system Technique Charts. Another method to ensure image quality, while reducing operator exposure and providing for patient dose optimization is the utilization of size-based technique charts or protocols. Technique charts should be unique to each x-ray unit and image receptor combination displaying suggested technique settings for a specific anatomical area along with the patient size (small, medium, large) for adults and children. These should be developed for both intraoral and extraoral imaging, listing the exam, patient size, along with adult and pediatric settings, and image receptor (film type, digital image receptor). Technique charts should be posted near the control panel where the technique is adjusted for each x-ray unit. With digital workstations, technique charts may also be readily placed on the workstation s desktop. When the x-ray unit is replaced, or an image receptor is added, the chart must be updated. An example of a technique chart is shown in Figure Clinical Image Display Monitors for Digital Imaging. An imaging display is a very important component in digital radiology. Most image display monitors are liquid crystal displays (LCD); newer LCD displays have light emitting diode (LED) backlights. Organic light 107

108 Sample Technique Chart Brand X Unit, Room 2 Brand Y Digital Image Receptor, Size 2 70 kvp, 7 ma Exposure Time, sec Child Adult (standard) Adult (large) Maxillary Incisor or Canine Premolar Molar Mandibular Incisor or Canine Premolar Molar Bitewing Anterior Posterior Occlusal Fig Sample technique chart indicating the x-ray unit, image receptor, kilovoltage, milliampere, and exposure time for various projections for adult patients of two sizes and for a pediatric patient

109 emitting diode (OLED) displays may soon be commercially available.. Image displays may be monochrome or color The amount of ambient light in an interpretation room has a significant impact on image interpretation; the ambient light levels must be controlled and only indirect lighting allowed Medical grade image displays have several advantages over off-the-shelf display monitors, including the capability of adjusting the brightness to compensate for variations in the intensity of the back light and ambient room light. If commercial off the shelf displays are used, it is important that periodic calibration be performed to maintain optimal performance (Section 5.2.6). A poor display quality may lead to inaccurate diagnosis and may result in inappropriate treatment for a patient

110 Intraoral Dental Imaging General Considerations Beam Energy Intraoral dental x-ray machines have been marketed with peak x-ray tube operating potentials ranging from 40 to >100 kvp. Units operating below 60 kvp result in higher than necessary radiation doses to the patient (AAPM, 2015) The operating potentials for intra-oral imaging equipment should be lower than for other dental imaging because the goal is to deposit x-ray photons into an imaging receptor just behind the teeth instead of an image receptor on the opposite side of the patient s head. Published data show no relationship between peak operating potential and effective dose to the patient with beam energies ranging from 70 to 90 kvp (Gibbs et al., 1988a). These data apply specifically to half-wave rectified intraoral dental x-ray machines. Similar beam energy spectra are produced by modern constant-potential machines operating up to 10 kv below the kilovoltage of full-wave or half-wave rectified machines. There is little to be gained from operating potentials higher than 80 kvp. In fact, higher kilovoltages decrease the inherent contrast in the images and are, therefore, detrimental to diagnostic image quality. Most contemporary intraoral x-ray units operate at a fixed operating potential in the 60 to 70 kv range Recommendation 61. The operating potentials of intraoral dental x-ray units shall not be <60 kvp and should not be >80 kvp Position-Indicating Devices A position-indicating device (PID) provides a visual aid to the operator in aligning the x-ray beam properly to the structure(s) being imaged. Position-indicating devices are attached to the x- ray tube head, are open-ended, and may be combined with higher atomic number materials that absorb scattered radiation arising from the patient, collimator, and filter. 110

111 Recommendation 62. Position-indicating devices shall be open-ended devices and should provide attenuation of scattered radiation arising from the patient, collimator or filter The length of the position-indicating device determines the source-to-skin distance. Short source-to-skin distances (or source-to-image receptor distances) produce unfavorable dose distributions (van Aken and van der Linden, 1966; White and Pharoah, 2014). They will degrade the sharpness of the images, and also produce excessive magnification or distortion of the image, sometimes limiting anatomic coverage Recommendation 63. Source-to-skin distance for intraoral radiography shall be at least 20 cm and preferably should be at least 30 cm Rectangular Collimation All medical and dental diagnostic x-ray procedures, except intraoral radiography, must be performed with the beam collimated to the area of clinical interest; in no case can it be larger than the image receptor (FDA, 2015). Positive beam-receptor alignment is required to ensure that all exposed tissue is recorded on the image. However, requirements and recommendations to date have permitted circular beams for intraoral radiography whose area, measured in the plane of the receptor, may be up to three times the area of a size 2 receptor, and four to five times the area of a size 0 receptor. Rectangular collimation of the beam to the size of the image receptor reduces the tissue volume exposed, especially that of the more sensitive parotid and thyroid gland tissues. This would reduce the effective dose to the patient by a factor of four to five, while simultaneously improving image contrast and overall diagnostic quality by reducing the amount of scattered radiation (Cederberg et al., 1997; Dauer et al., 2014; Freeman and Brand, 1994; Gibbs, 2000; Gibbs et al., 1988; Underhill et al., 1988; White and Pharoah, 2014) Due to the close tolerances between the x-ray beam and receptor sizes, it may be necessary to use a positioning device to assure complete coverage of the image receptor by the x-ray beam. A 111

112 variety of types, known as positioning devices, paralleling devices, or film or image receptor holders, are available. Rectangular collimation is recommended by the American Dental Association, the Food and Drug Administration, and the National Council on Radiation Protection and Measurement (FDA/ADA, 2015a; 2015b; NCRP, 2004) Rectangular collimators may be attached either to the position-indicating device or may be a part of the receptor-holding device. Receptor-holding devices are used to both stabilize intraoral image receptors in the mouth, and help align the position-indicating device on the x-ray tube head. Receptor-holding devices thus reduce artifacts from motion, misalignment, or other distortions while making radiographs. Receptor-holding devices should be used whenever possible It should be noted that ~50 % of the dental facilities in Great Britain use rectangular collimation (Holroyd, 2013). 2 Most academic institutions in the United States teach this technique but the proportion of dentists using rectangular collimation is much lower than in Great Britain, i.e., on the order of only 15 % (Farris and Spelic, 2015) Anatomy or the inability of occasional specific patients to cooperate, including some children, may make rectangular collimation and beam-receptor alignment awkward or impossible for some projections. The rectangular collimation requirement may be relaxed in these rare cases The amount of the patient s anatomy exposed to radiation with circular collimation is shown in Figures 7.1, 7.2, and 7.3. Figure 7.2 also shows that a significant amount of radiation exits the patient s head on the side opposite the x-ray tube. It should be noted that not all rectangular collimators produce the same size x-ray field at the skin surface. Collimators which attach to the end of existing round position indicating devices will provide smaller fields with longer position indicating device length. Some commercial rectangular collimators produce inherently larger Gray, J.E. (2015). Personal communication (DIQUAD, LLC, Steger, Illinois) 112

113 a. b Fig (a) This image shows the entry and exit exposed tissue volumes with round collimation (above) versus rectangular collimation (below). (b) The area of the primary beam exiting the round PID is three times greater than the area of a typical size 2 dental film. Thus, two-thirds of the primary beam without rectangular collimation is not used to create an image and is an unnecessary radiation exposure to the patient. Thus, the exposed volume is significantly reduced when rectangular collimation is used (adapted from White and Pharoah, 2014.)

114 Fig This image was created by holding a rare-earth screen-film cassette at the exit side of a patient s head. The film packet contained a lead foil and one Size 2 intraoral film, shown at the left. It is clear that the film packet absorbs only a small portion of the x-ray beam and that a large volume of the patient is exposed to radiation when a rectangular collimator is not used. This also provides an indication of the unnecessary amount of radiation exiting the patient on the side opposite the x-ray tube (images courtesy of J.E. Gray)

115 Fig Radiation fields at entry using round collimation versus rectangular collimation superimposed over a line drawing of a panoramic image. The exposed tissue area and resulting scatter are significantly reduced when rectangular collimation is used

116 radiation fields leading to less dose reduction in comparison with alternative rectangular collimators (Johnson et al. 2014) Recommendation 64. Rectangular collimation of the x-ray beam shall be used routinely for periapical and bitewing radiography, and should be used for occlusal radiography when imaging children with size 2 receptors Patient Restraint It may be necessary, in a limited number of cases, that uncooperative patients be restrained during exposure or that the image receptor be held in place by hand. A member of the patient s family (or other caregiver) should provide this restraint or receptor retention Recommendation 65. Occupationally-exposed personnel should not routinely restrain uncooperative patients and shall not hold the image receptor in place during an x-ray exposure Recommendation 66. Comforters and caregivers who restrain patients or hold image receptors during exposure shall be provided with shielding, e.g., radiation protective aprons, and should hold the film holding device. No unshielded body part of the person restraining the patient shall be in the primary beam Diagnostic Reference Levels and Achievable Doses For intraoral radiography, most published DRLs and ADs are based upon entrance air kerma (Hart et al. 2012; NCRP, 2012b). NCRP Report No. 172 (NCRP, 2012b) recommends for intraoral bitewing and periapical radiography a DRL of 1.6 mgy entrance air kerma, which was the 75 th percentile value for E-speed film in the 1999 NEXT dental survey (NCRP, 2012). NCRP Report No. 172 also recommends an AD of 1.2 mgy; this was the median dose for E-F film in a State of Michigan survey (LARA, 2015). NCRP Report No. 172 notes, It is recognized, and intended, that meeting this standard will most likely require dentists in the United States who use 116

117 D-speed film to convert to E-F- or F-speed film. Most digital image receptors should produce adequate images at entrance air kermas well below these DRLs and Ads, as shown by Table Best Practices Best practices in intraoral imaging are easily and inexpensively attained with commercially available equipment with three simple steps: using E-F- or F-speed films reduces the effective dose per image by 50 % or more compared to D-speed film; 2. using digital image receptors reduces the effective dose per image by 50 to 75 % compared to D-speed film; 3. using rectangular collimation reduces the effective dose per image by a factor of three to five, depending on receptor size, compared to round collimation Table 7.1 shows the potential for dose reductions by modifying receptor speed and collimation type. It is clear that simple changes can reduce patient effective dose by as much as 90 %, i.e., the patient is receiving only 10 % of the effective dose compared to the original technique! In addition to the significant dose reductions from the use of the fastest receptors and rectangular collimation, thyroid shielding provides additional protection, especially in children, where the thyroid is more sensitive to radiation carcinogenesis and is higher in the neck FDA Clearance of Dental Imaging Equipment X-ray units and digital imaging systems used in dental radiography must be cleared by FDA. The Internet allows purchasing such equipment from suppliers outside of the United States who may be providing items that have not been cleared by the FDA (Section 10.1)

118 2688 TABLE 7.1 Effective doses for intraoral dental radiographic views. a Technique Effective Dose (µsv) FMX b with D-speed film and round collimation 388 FMX with PSP or F-speed film and round collimation 171 FMX with CCD and round collimation (estimated) c 85 FMX with PSP or F-speed film and rectangular collimation 35 FMX with CCD and rectangular collimation (estimated) c 17 Two BWs with PSP or F-speed film and rectangular collimation a Adapted from Ludlow and Ivanovic (2008). b FMX = full mouth series = consists of 16 to 20 individual intraoral images c White and Pharoah (2014)

119 Conventional X-Ray Systems (Wall Mounted and Portable) General Information Intraoral dental x-ray sources are available in three different configurations. The x-ray source may be attached to an immovable fixture to the wall or ceiling of the operatory, a mobile unit supported by a mechanical stand on wheels, or a hand-held device not supported by any mechanical fixture (Section 7.3). Conventional wall- or ceiling-mounted dental x-ray sources are the most common type of dental x-ray units Equipment and Facilities The wall- or ceiling-mounted x-ray units should have the following components: a control timer unit mounted to the wall or connected by a retractable coiled cord and an articulating arm that connects the x-ray tube to the wall or ceiling fixture. The control unit provides options to select kilovoltage and milliamperage (if these are not fixed), and exposure time The control unit shall provide a visual and audible signal during the emission of x radiation. The x-ray exposure shall be controlled by a dead man s switch, i.e., the exposure must be terminated immediately on release of the switch. If the control unit is for a wall or ceiling mounted x-ray tube, the switch should be positioned behind a barrier so that the operator must stay behind the barrier during the exposure, i.e., the exposure switch must be at least 1 m from any outside edge of the barrier. If the system is a mobile x-ray unit, the control unit must be connected with a retractable cord and the working length of the cord shall be at least 2 m Although a wall- or ceiling-mounted unit is preferred, there may be circumstances where a mobile x-ray unit may be used. The advantage of such units are use in dental operatories that do not have x-ray units, operating and emergency rooms, or in temporary clinical facilities. A mobile unit shall have the same safety features as a wall- or ceiling-mounted unit

120 Recommendation 67. The stand of a mobile unit shall provide adequate support to the x-ray tube during travel and when the articulating arm is fully extended, and during x- ray exposure. The wheels or the casters shall be equipped with a foot brake to prevent motion of the unit during exposure There are circumstances, such as intra-procedure imaging in an operating room or images acquired on children who have to be seated in their parent s lap where it is not reasonable to have all persons cleared from the area during x-ray exposures. In such instances, the distance recommendations concerning positioning of the operator should be observed Recommendation 68. Only the patient and operator shall be in the area during an exposure unless special circumstances do not allow this Protection of the Operator and Shielding. Guidance for protection of the operator and shielding are in Section 4.5 and Appendix D Tube Head Positional Stability. The articulated arm that supports the x-ray tube head must be capable of achieving any position and angulation required for intraoral radiography, and maintaining it until the exposure is complete Recommendation 69. The tube head shall achieve a stable position, free of drift and oscillation, within 1 s after its release at the desired operating position. Drift during that 1 s shall be no greater than 0.5 cm Position-indicating Devices. The description and recommendations governing collimation and tube length of position-indicating devices are covered in Section Rectangular Collimation. The description and recommendations governing rectangular collimation are covered in Section

121 Hand-Held X-Ray Systems General Information Recent developments in x-ray sources for intra-oral dentistry have included systems that are designed to be held by the operator during use Optimal use of hand-held dental x-ray sources in intra-oral imaging requires adherence of equipment to certain design principles beyond those of wall-mounted systems. Traditional methods of shielding, including the utilization of fixed barriers and maximizing the source to operator distance, are not applicable to sources that are designed to be handheld. Indeed, the requirement that the operator never hold the x-ray source does not apply to devices that are designed to be hand-held. In these cases, due to the proximity of the operator to the x-ray source, increased radiation risks require additional design considerations. While the recommendations below are specific to hand-held equipment, other applicable design considerations such as Federal performance standards, and international standards (IEC, 2012) must still be observed. In particular, leakage radiation and backscatter radiation potentially pose a greater risk to the operator when using a hand-held x-ray source because the operator must be near the device for operation. In order to mitigate these risks, additional shielding is incorporated into the design The first contemporary hand-held dental x-ray units were introduced in 2005 and today there are over 17,500 in use in the United States (with a growth rate of 15 % y 1 ). Initially the sale of these units met resistance from the regulatory community due to an old rule of thumb, sometimes in regulations and other times not, that one should never hold the x-ray tube. This is a valid rule for conventional x-ray tubes due to leakage radiation from the tubes. However, properly designed hand-held dental x-ray units are specially shielded to minimize the dose to the hands and body of the operator (Gray et al., 2012). Many papers have been published by different investigators demonstrating the safety and effectiveness of a properly shielded hand-held dental x-ray unit (Danforth, 2009; Goren, 2008; Gray et al., 2012)

122 Figure 7.5 (left) shows a hand-held dental x-ray unit, cleared by FDA for sale in the United States, that has a leaded-acrylic x-ray shield affixed to the front. This shield protects the operator s hands and body from backscattered radiation when properly oriented. Figure 7.5 (right) shows the operator using this hand-held unit to make an intraoral dental radiograph. The zone that is protected by the leaded acrylic shield can be clearly seen (the green area as opposed to the red area) Advantages of Hand-Held X-Ray Units. Hand-held units can often be used in environments or circumstances where use of fixed or mobile units is either extremely cumbersome or impossible, such as operating rooms, emergency rooms, nursing homes, and remote locations, and intraoperative endodontic and pediatric dental imaging. In addition, they are quite useful in forensic investigations and in the identification of remains during a major catastrophe. The following lists some of the other features and advantages: They are especially helpful in patients with special needs and in surgical operatories where traditional x-ray machines cannot be easily used during certain procedures. Hand-held x-ray units provide low radiation exposure to the operator if appropriate operating instructions are followed. The radiation dose is comparable to wall-mounted x- ray machines. They are capable of producing sharp images even with mild operator movement. They are easy to operate and position. The quality of the radiographs made from hand-held devices is comparable to traditional wall-mounted devices. One hand-held unit can be shared between two or more rooms Disadvantages of Hand-Held X-ray Units. There are disadvantages to hand-held x-ray units. Some states may impose restrictions on their use. Some can be operated without a backscatter shield (none is provided or it can be removed), which increases the radiation dose to the operator. Other potential disadvantages include:

123 Fig A hand-held unit cleared by FDA for sale in the United States. (Left) unit showing leaded-acrylic shield on front. (Right) leaded-acrylic shield provides protected zone (in green) for the user compared to no protection (red-to-pink). In an actual patient image acquisition, rectangular collimation would be used. In order to best illustrate the effect of the acrylic shielding, rectangular collimation was not included in this illustration

124 Misalignment between the unit and the film or receptor, especially if a beam-guiding device is not used. The operator must put down the hand-held unit down while positioning film or image receptor in the patient s mouth, thus increasing the risk of cross-contamination. Some are more expensive than traditional x-ray units. If used incorrectly there can be increased dose to the operator. Some are heavy and can be awkward and inconvenient to use; using such a machine for a long time can cause operator fatigue. Some of the units require connection to a power source which limits their mobility. While the batteries in the units are capable of powering multiple exposures, they require an electrical source for recharging and it is possible that there might not be sufficient power for multiple exposures from a single charge, especially in remote sites. Infection control is often difficult, especially when a plastic bag is used as the barrier. Some of the units, especially those available on the Internet, are not cleared by the FDA for sale in the United States; however, such units are available in the market for purchase at very low, attractive prices. Such units may exhibit the following problems: o high leakage radiation; o no dead-man switch ; o actual (measured) kv is far below the indicated value; o no audible signal of x-ray exposure; o poor quality components more likely to break down quickly; and o low image quality due to low x-ray output and resultant long exposure times to acquire a diagnostic image Individuals responsible for the purchase of hand-held x-ray units must be certain that the unit has been cleared by the FDA. This will be indicated by the label on the device, illustrated in Figure Safety Issues with Improper Handling of Hand-Held X-Ray Equipment. The design of hand-held x-ray equipment presents different challenges for protecting patients, operators, and 124

125 the public from unnecessary radiation exposure. In particular, device positioning, weight, and security and access controls introduce additional radiation safety issues that must be considered when using hand-held x-ray equipment Many of the assumptions about positioning that are made for wall-mounted systems are not valid when using a hand-held x-ray system. While permanent installation for a wall-mounted system allows assumptions to be made about minimum distances between the x-ray equipment and members of the public, and permanent shielding to be placed between the source and other patients, these are not always true for hand-held systems There is no control for the distance between the source and members of the public for handheld x-ray systems. The operator must ensure that there is proper distance and shielding between the source and members of the public. When used in a dental facility to replace a wall-mounted system, using the hand-held system in the same location as a conventional x-ray machine will provide sufficient radiation protection for members of the public. More information is needed to develop guidelines for equipment used outside of the dental office where there is most likely inadequate shielding design The hand-held nature and weight of these systems also introduces risks due to operator fatigue from holding the device for multiple imaging exams. Operator fatigue can lead to poor positioning of the system, which can lead to poor quality radiographs and the need for repeated exposures. Additionally, fatigue could cause the operator to hold the device closer to the chest, possibly moving the backscatter shield sufficiently back to expose parts of the operators head. Thus, operators of hand-held x-ray equipment must have the physical ability to hold the system in place for all exams. This should be taken into consideration while evaluating operator workloads to minimize the need for repeat exposures to patients Recommendation 70. Operators of hand-held x-ray equipment shall have the physical ability to hold the system in place for multiple exposures

126 Additional training is necessary for all operators of hand-held x-ray equipment to introduce them to the proper operation of these units. This training should include topics such as proper positioning with the hand-held unit, variations in positioning which improve radiation safety of staff, and safe areas relative to the leaded-acrylic shield and the necessity for its use Recommendation 71. Manufacturers should provide a training program for users of hand-held equipment to emphasize the appropriate safety and positioning aspects of their unit Many hand-held systems are designed such that the exposure button can be found intuitively by nontrained users. This benefits operators and reduces the amount of training necessary, but also increases the risk of use by a nonqualified operator, and even children. Operators and manufacturers can both take steps to mitigate this risk Methods to prevent the unauthorized use of hand-held x-ray units should be implemented, e.g., a key lock, or a software key that the operator would be required to enter before the device could be activated. In addition, an exposure counter would provide information about the total number of exposures and, along with an exposure log, would allow the practitioner to monitor the use of the equipment Recommendation 72. Operators shall store hand-held x-ray equipment such that it is not accessible to members of the public when not in use Recommendation 73. Manufacturers of hand-held x-ray equipment shall incorporate either hardware or software interlocks on their devices to prevent unauthorized use. Hardware interlocks may include physical keys or locks necessary for operation while software interlocks may include password restrictions Exception to Never Hold the X-Ray Unit. Traditional radiation protection recommendations instruct users to never hold the x-ray unit. The rationale behind this recommendation is that leakage radiation from the x-ray unit and backscatter radiation expose 126

127 the operator to unnecessary radiation. This recommendation is both unnecessary and impractical for properly designed hand-held x-ray systems that have been FDA-cleared. Properly designed hand-held x-ray systems include sufficient shielding around the x-ray unit, and backscatter shielding to protect the operator and mitigate the traditional risks associated with holding the x- ray unit. Properly designed equipment should also include identification of the areas in which it is safe for the operator to stand during exposures based on the specific protective shielding in the device design Hand-held systems that are not properly designed and not FDA-cleared present the same or greater risks as traditional x-ray systems and should not be used. More information can be found in Section to determine if a particular unit is properly designed and labeled Recommendation 74. Instructions supplied with hand-held x-ray equipment shall include identification of the areas in which it is safe for the operator to stand during exposures based on the specific protective shielding in the device design Equipment Hand-held x-ray units must include safety interlocks to prevent unauthorized exposures, a clear shield on the end of the PID to protect the operator from scattered radiation, and additional shielding to reduce the leakage radiation to the operator. Some states are promulgating specific hand-held dental radiography regulations; dentists, operators and qualified experts must know the current regulations in their localities Backscatter Shield. Since the operator is standing near the patient there is a potential for increased exposure from back-scattered radiation Recommendation 75. Hand-held x-ray devices shall include a clear, external, nonremovable, radiation protection shield containing a minimum of 0.25 mm lead equivalence between the operator and the patient to protect the operator from backscatter radiation. 127

128 Leakage Radiation. Some hand-held dental x-ray units fail to meet FDA standards. In February 2012, the FDA issued a Safety Communication regarding units made overseas and being sold on the Internet without FDA clearance (FDA, 2012). In June 2012, the Health Protection Agency (HPA) of the United Kingdom issued an alert regarding similar equipment and published a report of their measurements (HPA, 2012). This device was neither cleared by the FDA (Figure 10.1) nor does it carry a CE mark. In December, 2014, a similar report was published in the United States concerning yet another similar system (Mahdian et al., 2014) The HPA report indicates that the unit they evaluated (Figure 7.6) had several problems including: substantial radiation leakage from the x-ray source in the front of and behind the unit (Figure 7.7a and 7.7b); 2. no shielding is provided to protect the operator from backscattered radiation (Figure 7.6); 3. the operator s hands receive a dose of 7.5 mgy for each x-ray exposure; 4. exposure times were long, e.g., 3 s, which could result in motion and blurred images; and 5. operator annual dose for 100 x-ray exposures per week was estimated at 40 Sv equivalent dose to the hands and 30 msv effective dose to the body Radiation Protective Equipment and Personal Radiation. Hand-held systems with internal and backscatter shielding have been shown (Danforth, 2009; Goren, 2008; Gray et al., 2012) to be effective in protecting the operator from radiation exposure. Operator exposure when using these hand-held systems according to the manufacturer s instructions is generally comparable to the operator exposure associated with wall mounted systems. Due to the effectiveness of internal and backscatter shielding of properly designed equipment, personal protective shielding is not necessary for the operator of hand-held x-ray units

129 Fig Example of hand-held dental x-ray system, not cleared by FDA. This device, manufactured outside the United States, does not carry a CE mark and has not been cleared by the FDA. It is marketed under several names. (This device was sold in the United States even though it was not FDA cleared.)

130 Leakage Primary a b Fig (a) Radiographic image showing the radiation from the front of a non-fda cleared hand-held x-ray unit. In addition to the primary beam there is a substantial amount of leakage radiation also exposing the patient. (b) Radiographic image showing the radiation leaking from the back of this hand-held x-ray unit which would expose the user to unnecessary radiation (courtesy of the Health Protection Agency of the United Kingdom)

131 Recommendation 76. The operator of a hand-held x-ray unit shall not be required to wear a personal radiation protective garment Likewise, there is no need for personal radiation monitoring with hand-held x-ray equipment as long as the whole-body effective dose to the operator is below 1.0 msv y -1. It is prudent for operators to use personal monitors when initially using hand-held x-ray units (e.g., for six months) to confirm their radiation exposure levels Appropriate Use of Hand-Held X-Ray Machines in Dental Offices. Comparison to European Recommendations. The Heads of the European Radiological Protection Competent Authorities (HERCA) June, 2014 position statement on the use of hand-held x-ray equipment discourages their use except in special circumstances such as nursing homes, residential care facilities, or homes for persons with disabilities; forensic odontology; and military operations abroad without dental facilities (HERCA, 2014). The NCRP feels that the HERCA criteria are overly restrictive and that there are additional circumstances where the use of hand-held x-ray equipment may be suitable or advantageous (Section ). The Committee anticipates the possibility that as hand-held x-ray equipment becomes less expensive, easier to use, and maintains or improves its safety characteristics, these units may supplant fixed or mobile x-ray equipment in general dental practice Position-Indicating Devices The description and recommendations governing collimation of position-indicating devices are covered in Section Hand-held x-ray units have built-in position indicating devices of various lengths Rectangular Collimation Rectangular collimators are available as a part of the receptor-holding device on hand-held x-ray systems. 131

132 Recommendation 77. Rectangular collimation shall be used with hand-held devices whenever possible The description and recommendations that apply to rectangular collimation are covered in Section

133 Extraoral Dental Imaging Panoramic General Information Panoramic dental units produce a curved-surface tomogram of the oral and maxillofacial image. The tomographic focal trough follows the curved contours of the jaws, in general extending from ear to ear and from below the chin to the lower portion of the orbits. Despite the advantage of imaging the entire dentomaxillofacial anatomy in one sweep, there are inherent limitations in the anatomical representations due to the very motion necessary to produce the panoramic image. Vertical image magnification is independent of horizontal magnification. The degree of magnification varies with position in the dental arch. This image distortion varies with anatomic area in a given patient and from patient to patient using the same panoramic x-ray machine. Furthermore, repeat images of the same patient may show differing distortion because of slight differences in patient positioning. In addition, image resolution is limited by the imperfect movement of source and image receptor required for the tomographic technique. Resolution with panoramic imaging (both film and digital) is less than with intraoral imaging (film and digital, respectively), resulting in diminished diagnostic accuracy of incipient caries, beginning periapical lesions, or marginal periodontal disease (Farman, 2007; Flint et al., 1998; Rumberg et al., 1996; White and Pharoah, 2014) Active development of improved projection geometry, digital tomosynthesis and the use of photon-counting detectors in panoramic imaging are likely to appear soon and should improve the quality and utility of panoramic imaging in dentistry Diagnostic Reference Levels and Achievable Doses. For panoramic imaging, NCRP Report No. 172 uses the air kerma-area product as the dose metric for its recommended DRL and AD. NCRP Report No. 172 recommends a DRL of 100 mgy cm 2 and an achievable dose-area product of 76 mgy cm 2 (NCRP, 2012b). Both are based upon European surveys. 133

134 Bitewings from Digital Panoramic Machines. Numerous manufacturers of panoramic equipment have devised imaging techniques that produce an image similar to a bitewing projection. The use of these images may be indicated for patients that cannot tolerate an intraoral bitewing radiograph. Situations such as hyperactive gag reflex, trismus, or large tori are suggested as indications for the use of these extraoral bitewings. Currently, there is only one study comparing the diagnostic efficacy of specific panoramic bitewing technique images with intraoral images and claimed that the intraoral bitewings were superior in caries detection. The data analysis was not robust, and, therefore, the conclusions are suggestive but equivocal (Kamburog-lu et al., 2012). Further studies are needed in order to make specific recommendations on the use of panoramic bitewing programs for caries detection, and likely periodontal evaluations Equipment and Facilities Panoramic dental units employ a stationary anode radiographic x-ray tube operating at tube peak potentials in the 70 to 100 kvp range. These systems utilize a narrow vertical collimator to produce a correspondingly narrow x-ray beam that passes through the patient. During a panoramic x-ray exposure the moving x-ray beam paints the image on the image receptor as the x-ray tube rotates around the patient. In the case of film-screen imaging, the screen-film cassette shifts during panoramic motion, resulting in exposure of the entire film. This produces a curvedsurface tomogram of the dentomaxillofacial structures. Panoramic x- ray beams must be no larger than the area of receptor exposed to the beam at any point in time. This area is defined by the slit collimator at the tube head Digital panoramic images can be produced by replacing the screen-film cassette with a cassette containing a photostimulable phosphor plate. Direct digital panoramic x-ray units utilize a narrow CCD or CMOS receptor array to create the familiar panoramic image. As with any digital imaging modality, digital panoramic x-ray unit displays allow the user to vary the brightness and contrast appearance of the image by adjusting window and level settings. Some 134

135 direct digital panoramic units allow adjustment of the position of the image layer after the image has been acquired reducing the impact of patient positioning on image quality Recommendation 78. The x-ray beam for rotational panoramic tomography shall be collimated such that its vertical dimension is no greater than that required to expose the area of clinical interest and shall not exceed the size of the image receptor Older machines were designed for use with medium-speed calcium tungstate screen-film systems. In some cases the required reduction in x-ray output for use with high-speed rare-earth screen-film systems may only be accomplished by electronic modifications or addition of filtration at the x-ray tube head. Electronic modifications are permitted by the manufacturer if the modified device is cleared by the FDA through the 510(k) process. A manufacturer can modify an installed device in this manner. Added filtration, unless compensated by lower kilovoltage, hardens the beam spectrum, resulting in decreased image contrast. The dentist must be aware of these limitations in selecting and maintaining panoramic equipment or prescribing panoramic examinations. Otherwise, the limited diagnostic information obtained from the panoramic image may necessitate additional imaging. Periapical views alone may be adequate Recommendation 79. The fastest imaging system consistent with the imaging task (equal to or greater than ANSI 400 speed, or digital) shall be used for all panoramic radiographic projections Power for panoramic units may be an important factor. Panoramic units should not be on the same power supply as high power devices, e.g., elevators and air conditioners. Operation of other high power consuming devices can cause a fluctuation in the voltage to the panoramic unit and, hence, a fluctuation in the kilovoltage output Recommendation 80. Panoramic machines shall be on a dedicated electrical circuit

136 Cephalometric General Information Cephalometric equipment provides for positioning (and repositioning) of the patient together with alignment of beam, subject and image receptor. The source-to-skin distance is on the order of 150 cm or more, minimizing geometric distortion (magnification) in the image. It is frequently useful for the cephalometric image to show bony anatomy of the cranial base and facial skeleton plus the soft-tissue outline of facial contours, requiring image receptors of wide latitude. Additional filtration can further enhance soft tissue contours on the same image as the bone details (Section 8.2.2) Diagnostic Reference Levels and Achievable Doses. For cephalometric radiography, NCRP Report No. 172 provides DRLs and ADs for entrance air kerma and air-kerma area product, both for the lateral projection. For the DRL, the report recommends, for the entrance air kerma, 0.14 mgy and for the air-kerma area product, 26.4 mgy cm 2 for children and 32.6 mgy cm 2 for adults. For ADs, the report recommends for the entrance air kerma 0.09 mgy and for the air-kerma area product 14 mgy cm 2 for children and 17 mgy cm 2 for adults Equipment and Facilities The area of clinical interest in cephalometric radiography is usually significantly smaller than the image receptor. Thus, collimation to the size of the image receptor does not meet the intent of restricting the beam to image only those structures of clinical interest (FDA/ADA, 2015a). The central axis of the beam is usually aligned through external auditory canals, which are positioned by the ear rods of the cephalostat. Imaging of structures superior to the superior orbital rim, posterior to occipital condyles, and inferior to the hyoid bone is clinically unnecessary. Therefore, the beam should be collimated such that these areas are shielded from exposure. Thus, the desired collimation is asymmetric, and the central axis of the beam is not centered on the image receptor. Further, it is usually desirable to image the soft-tissue facial profile along with the osseous structures of the face; this is accomplished by reducing exposure to the anterior soft 136

137 tissues using filters that are placed between the x-ray source and the patient (Freedman and Matteson, 1976; Tanimoto, 1989). Placement of filters at the image receptor instead of at the x- ray source does not reduce the dose to the patient and is inappropriate Recommendation 81. The fastest imaging system consistent with the imaging task (ANSI 400 speed or greater, or digital) shall be used for all cephalometric radiographic projections Recommendation 82. X-ray equipment for cephalometric radiography shall provide for asymmetric collimation to limit the beam to the area of clinical interest Recommendation 83. Filters for imaging the soft tissues of the facial profile together with the facial skeleton shall be placed between the patient and at the x-ray source rather than at the image receptor

138 Cone-Beam Computed Tomography General Information Dental cone-beam computed tomography (CBCT) has expanded the field of oral and maxillofacial imaging enhancing diagnostic information for the dental clinician through threedimensional volumetric image data of dental and maxillofacial structures (ADA 2012; Tyndall et al 2012). Since its introduction in 1997, CBCT has gained an increasing role in dentistry, transitioning from two- to three-dimensional imaging. By providing diagnostic images without magnification, distortion, superimposition, and misrepresentation of structures, CBCT imaging provides increased diagnostic accuracy, enhancing treatment outcomes. CBCT is also used by head and neck radiologists and ear-nose-throat, or otolaryngologist, physicians to assess midface, and middle and inner ear, throat, and other skull base structures (Cakli et al., 2012; Miracle and Mukherji, 2009a; 2009b) The value of CBCT image data may be augmented with sophisticated software applications which enhance images and permit merging of images with complementary data sets. An example of this is the combination of CBCT images with photographic images of the teeth and soft tissues acquired with intraoral cameras. Merging of these data sets provides an accurate representation of the hard and soft tissues and their relationship to each other, enabling visualization of not only implant position, but also the final restoration. In addition, CBCT scans through computer aided design and manufacturing (CAD-CAM) technology can provide surgical guides for implant placement. Several CBCT equipment manufacturers and software vendors provide the capability of integrating 3D scans with CAD-CAM technology by CBCT impression scanning of conventional dental impressions so that crowns can be designed and milled chairside Many CBCT systems present an appearance that is similar to panoramic dental units. Indeed there are many similarities, including patient positioning, approximate imaging time, kilovoltage and milliamperage. From an imaging perspective, the most substantive difference is the availability of reconstructed images of various slice thicknesses, viewable in many planes, 138

139 orientations or 3-dimensional renderings. From a safety perspective, substantial differences in the size and shape of the x-ray beam affect the dose to the patient, dose to the operator, and people who may be nearby. Median effective dose imparted by a standard CBCT examination with a medium field of view is ~107 µsv. Typical conventional panoramic doses are 20 % of this value (Ludlow et al., 2015) CBCT scanners differ from conventional CT scanners [multi-detector CT (MDCT)] primarily in image data acquisition. In a conventional CT scanner, the x-ray beam emerges from the x-ray source as a flat fan beam. Data is acquired as a series of consecutive slices of the patient s head acquired from multiple rotations of the x-ray source around the patient. In some MDCT scanners the width of the beam can be as large as 160 mm, enabling acquisition of individual organs in a single sweep. In contrast, the x-ray beam in a dental CBCT scanner diverges from the x-ray source as a cone or pyramid. Data is acquired as a series of area projections made with small angular differences as the beam rotates around the patient s head. Scanners acquire image data (termed basis images) through a single rotation of at least 180 degrees and up to 360 degrees around the patient s head. Images are reconstructed through algorithms, producing threedimensional images. Due to hardware differences CBCT scan acquisition times may range from 10 to 70 s. Similar volume sizes may be acquired with MDCT, while decreasing acquisition times to as little as 1 s or less. The radiation dose to the patient from CBCT may be up to 10 times less than that from a similar MDCT examination; however, some CBCT units and examination protocols produce doses comparable to MDCT scans (Ludlow and Ivanovic. 2008) and, in some cases, doses which may exceed those of MDCT scans (Ludlow et al., 2014) Most CBCT systems employ fixed anode x-ray tubes similar to those in panoramic x-ray machines, operating in the 70 to 100 kvp range. Instead of a narrow vertical aperture, CBCT systems employ collimation that permits larger area exposures. These beam limiting devices have varying degrees of adjustment selectable by the operator. Several manufacturers provide systems with a choice of several beam sizes, allowing the operator to select both beam height and width appropriate for few teeth or the full maxillofacial region

140 CBCT image receptors are essentially direct digital radiography receptors that employ flat panels. The larger image receptors are generally capable of collecting smaller x-ray fields of view Dose Comparisons for CBCT and MDCT Machines Although CBCT radiation doses are usually less than those produced during MDCT, the radiation doses to tissue are usually higher than those of conventional dental radiographic modalities. The effective dose of an optimized CBCT examination is 2 to 5 % of a conventional CT of the same region, but approximately seven times greater than that from a panoramic image (Ludlow and Ivanovic, 2008) Table 9.1 shows approximate effective doses from CBCT and MDCT units, operating with different fields of view. The values are averaged from wide ranges of exposures, depending on the specific units measured and the acquisition parameters Recommendation 84. CBCT should be used for cross sectional imaging as an alternative to conventional computed tomography when the radiation dose of CBCT is lower and the diagnostic yield is at least comparable Doses for CBCT devices vary widely, but median, typical protocol adult doses are ~60 µsv for small FOVs, 107 µsv for medium FOVs and 151 µsv for large FOVs (Figure 9.1). Similar patterns of increased dose with increased FOV size are seen for child phantom exposures (Figure 9.2) In summary, Figures 9.1 to 9.3 show that the effective dose varies by FOV size for both adults and children. Furthermore, these also show the relative contributions of bone marrow, brain, and thyroid decrease with decreasing FOV size. However, the relative contributions of salivary gland and remainder tissues increase with decreasing FOV size

141 TABLE 9.1 Approximate effective doses from CBCT and MDCT examinations. Examination a Effective Dose (µsv) CBCT small FOV 60 CBCT medium FOV 107 CBCT large FOV 151 MDCT mandible (isotropic voxels) 427 MDCT jaws 697 MDCT head 1, a CBCT doses are from Ludlow et al., MDCT doses are from Tables F1 and F2 in Appendix F 141

142 Fig Effective doses of typical CBCT examinations by field of view size for adult phantom exposures. Median and inter-quartile spread are shown (Ludlow et al., 2015)

143 Fig Effective doses of typical CBCT examinations by field of view size for child phantom exposures. Median and inter-quartile spread are shown (Ludlow et al., 2015)

144 Fig Relative organ contributions to effective dose by FOV size (Ludlow et al., 2015)

145 Recommendation 85. CBCT examinations shall use the smallest field of view (FOV) and technique factors that provide the lowest dose commensurate with the clinical purpose Use of Simulated Bitewing, Panoramic, and Cephalometric Views from CBCT Data Cephalometric images produced with conventional x-ray equipment using rare earth screens and matched film or digital technologies produce typical adult effective doses around 5 µsv. Standard panoramic doses vary for different devices, but typical adult doses are between 15 and 25 µsv While bitewing projections, panoramic image layers, and cephalometric projections can be reconstructed from a CBCT image volume, low resolution and artifact from nearby metal restorations limit the usefulness of these reconstructions for diagnosis of dental caries. In addition, radiation doses are substantially greater than needed to produce conventional panoramic and cephalometric images (Table 9.2). As such, they cannot replace the use of conventional bitewing, panoramic, and cephalometric images in dental practice Table 9.2 presents patient effective doses reported in the literature for CBCT, compared with other common x-ray imaging exams. Recommendation 86. CBCT examinations shall not be obtained solely for the purpose of producing simulated bitewing, panoramic, or cephalometric images Number of CBCTs in the United States and Growth Rate The just-completed 2015 Nationwide Evaluation of X-Ray Trends (NEXT) survey examined the use of x-ray diagnostics in dentistry (Farris and Spelic, 2015). Preliminary analysis estimates there are 5,500 dental CBCT units in the United States. It also estimates 300,000 pediatric CBCT examinations annually and 3,876,000 adult and adolescent CBCT examinations annually

146 TABLE 9.2 Comparison of effective doses for CBCT. MDCT, and conventional radiographic examinations (EC, 2012). Modality Median (µsv) Range (µsv) CBCT, dento-alveolar CBCT, craniofacial ,073 Intraoral radiograph <1.5 Panoramic radiograph Cephalometric radiograph <6.0 MDCT maxillo-mandibular 280 1,

147 CBCT in dentistry has grown rapidly over the past decade through its features of short scanning times, increased diagnostic yield relative to radiation exposure, high resolution, and geometric accuracy. A 2011 study found 15 different manufacturers offer 24 CBCT models in the United States and many more worldwide (Ludlow, 2011). This suggests an impressive continuing demand for this technology. With its increasing application in dentistry, there has been a focus to develop guidelines for its safe and effective use, along with the development of selection criteria, quality assurance programs and clinical optimization in through evidence based research. National and international groups have provided basic principles (White and Pharoah, 2014), selection criteria and professional guidelines (EC, 2012) for CBCT in dentistry. Position statements (AAE/AAOMR, 2011; AAOMR, 2013; Tyndall et al., 2012) and CBCT guidance documents (EC, 2012) have been developed by dental specialty organizations Efforts Regarding CBCT in Europe SEDENTEXCT and Evidence-Based Guidelines The SEDENTEXCT project of the European Commission (2008 to 2011) was a widespread effort by stakeholders throughout the European Union (partnership from the United Kingdom, Greece, Romania, Belgium, Sweden, and Lithuania) to develop guidelines for the safe and effective use of cone beam CT in maxillofacial imaging. The final report, entitled Radiation Protection No 172. Cone Beam CT for Dental and Maxillofacial Radiology. Evidence-Based Guidelines was published in 2012 (EC, 2012) and contains exhaustive data and discussion on all aspects of CBCT imaging, including radiation dose and risk, basic principles of CBCT imaging, selection criteria, quality assurance, and protection and training of staff. Additionally, a CBCT quality assurance protocol and phantom were developed. The reader is referred to this robust document for further details as well as the SEDENTEXCT website A comprehensive review of CBCT indications and use has been published recently (Horner et al., 2015)

148 Patient Selection Criteria for CBCT The CBCT examination is a complementary examination to, not a replacement for, twodimensional imaging modalities. Just as for other dental radiographic examinations, justification for each patient should be based on their imaging history and the diagnostic yield not achievable with the 2D modalities. The examination is justified if the anticipated diagnostic yield outweighs the risks associated with radiation (AAOMR, 2008; ADA, 2012; EADMFR, 2009; Farman and Scarfe, 2006; White, 2009). CBCT should only be used when the question for which the imaging is required cannot be answered adequately by conventional, lower dose dental radiography, applying the ALARA principle (NCRP, 2003) Prior to the acquisition of a CBCT examination, a dental examination by the ordering provider should be completed, with a review of the patient s medical history, as well as the medical and dental imaging history. Previously acquired dental and medical imaging, which falls short of yielding the necessary clinical information, may justify the need for the CBCT examination (ADA, 2012; Farman and Scarfe, 2006). The decision about the clinical indication for CBCT is the professional determination of the treating clinician Recommendation 87. CBCT shall not be used as the primary or initial imaging modality when an alternative lower dose imaging modality is adequate for the clinical purpose Some of the evidence-based specific indications for CBCT imaging follow Implants. The initial overall evaluation of a potential dental implant patient should be completed using panoramic imaging. CBCT is widely considered as the imaging modality of choice for preoperative, cross-sectional imaging of potential implant sites (Tyndall et al., 2012). CBCT demonstrates bone volume, quality or topography, and relationships to vital anatomical structures such as nerves, vessels, nasal floor, and sinus floors. Implant planning using CBCT must take into consideration the restorative process for which implants are being planned. For this reason, when treatment of multiple implant sites is being planned, radiographic guides 148

149 should be considered prior to any CBCT for implant planning. This also insures that patient radiation dose is optimized when planning multiple sites CBCT may also be considered when clinical conditions suggest a need for augmentation or site development before placement of implants. CBCT should be considered if bone reconstruction and augmentation procedures have been performed. In the absence of clinical signs or symptoms, intraoral periapical imaging should be used for the postoperative assessment of implants. Panoramic radiographs may be indicated for more extensive implant therapy cases. CBCT should be considered if implant retrieval is anticipated (ADA, 2012; Almog et al., 1999; Benavides et al., 2012; Ebrahim et al., 2009; Harris et al., 2012; Tyndall and Rathore, 2008; Tyndall et al., 2012; Wang et al., 2011) Use of CBCT immediately post-operatively may be indicated if the patient presents with implant mobility or altered sensation, particularly if the fixture is in the posterior mandible (Harris et al., 2012; Tyndall et al., 2012). CBCT imaging is not indicated for the periodic review of clinically asymptomatic implants Oral and Maxillofacial Surgery. Many surgical procedures involving bony components of the jaws and maxillofacial structures may benefit from CBCT. CBCT images often provide valuable information for surgical planning and follow-up. Before ordering CBCT imaging, the clinician should evaluate other imaging modalities requiring less radiation that may provide sufficient diagnostic information. Where soft tissue evaluation is essential to diagnosis and treatment planning, CBCT is inappropriate because of poor soft tissue resolution. In such circumstances, MDCT, MRI, or ultrasound are likely to be more appropriate and efficacious In treatment planning the surgical removal of third molars or other impacted teeth, conventional imaging may suggest a direct inter-relationship between the teeth and surrounding key anatomic areas such as the maxillary sinus, adjacent teeth, and mandibular nerve. Limited CBCT may be indicated for pre-surgical assessment of an impacted or unerupted tooth as an adjunct to conventional imaging (Becker et al., 2010; Neugebauer et al., 2008; Suomalainen et al., 2010; White, 2008). 149

150 Limited-volume, high-resolution CBCT may also be indicated for evaluation of intraosseous pathological entities when the initial imaging modality used for diagnosis and staging does not provide satisfactory three-dimensional information (Rosenberg et al., 2010; Simon et al., 2006; White, 2008). In evaluating lesions in the maxilla and mandible, intraoral or panoramic radiographs show only two dimensions of the lesion. CBCT imaging may provide additional information on the extent of the lesion, cortical expansion, internal or external calcifications, and proximity to teeth as well as other vital anatomy. In surgical planning, a lesion must be measured from different angles. CBCT measurements, when compared to the gold standard dry skull have been shown to be acceptably accurate with <1 % error (Ludlow et al., 2007; Stratemann et al., 2008) Initial assessment of a simple dental or jaw fracture, and in some cases complex jaw fracture, may also be achieved with periapical or panoramic radiographs. However, vertical root fracture (Wang et al., 2011) or multiple jaw fractures (Palomo and Palomo, 2009; Shintaku et al., 2009) may be better visualized with CBCT images. In such cases, CBCT may be a valid alternative imaging modality to MDCT, considering image quality and radiation dose (Tyndall, 2008; White, 2008) CBCT may be utilized for pre-operative orthognathic surgical planning (Farman and Scarfe, 2006). DICOM data from CBCT can be used to fabricate physical stereolithographic models or to generate virtual 3D models (O Neil et al., 2012), which have been useful for orthognathic assessment of morphology, spatial relationship, and growth and developmental anomalies. The 3D reconstructions from CBCT are useful in the diagnosing and treatment planning of facial asymmetry cases. Follow-up CBCT imaging is useful in evaluating the success of orthognathic surgery, as well as to measure the displacement of the surgical segments in all three orientations (Cevidanes et al., 2007) Periodontal Indications. CBCT is not indicated for routine evaluation of the periodontium. When clinical examination and conventional imaging studies do not provide the information needed for the management of infra-bony defects and furcation lesions, limited 150

151 volume, high resolution CBCT may be indicated (Tyndall et al., 2008; Vandenberghe et al., 2008; Walter et al., 2010; White, 2008). In CBCT fields of view that include images of teeth, periodontal bone should be evaluated for periodontal disease Endodontic Indications. CBCT is not indicated as a standard method for demonstration of root canal anatomy. Limited volume, high resolution CBCT may be indicated when conventional intraoral imaging provides inadequate information, contradictory clinical signs and symptoms are present, evidence of inflammatory root resorption, internal resorption, suspected root fracture, combined periodontal-endodontic lesions, perforations or atypical pulp anatomy (AAE/AAOMR, 2011; 2015; Tyndall et al., 2008). In CBCT fields of view that include images of teeth, periradicular bone should be evaluated for periapical disease Temporomandibular Joint Indications. The high spatial resolution of CBCT makes it ideal for detailed evaluation of osseous changes in the temporomandibular joint. While panoramic imaging often gives a limited overview of the status of these bone components, CBCT is indicated when a more detailed examination is needed. This would be most often indicated for severity assessment of arthritides, evaluation of erosive or proliferative bone lesions, or intracapsular condylar trauma (Alexiou et al., 2009; dos Anjos Pontual et al., 2012; Librizzi et al., 2011; Palomo and Palomo, 2009) CBCT is not appropriate for evaluation of internal derangements due to its poor contrast resolution and inability to demonstrate the soft tissue structures (Marques et al., 2010) Caries Diagnosis Indications. CBCT is not an acceptable diagnostic examination for occlusal (Rathore et al., 2012) or proximal (Wenzel et al., 2014) carious lesions (Section 9.1.2) Sinonasal Evaluation Indications. Spatial and contrast resolution of CBCT is acceptable for evaluating osseous and gross soft tissue changes of the sinusonasal complex (Tadinada, 2015b; Xu et al., 2012). In particular, details of the integrity and configuration of the borders of these structures are clearly shown on CBCT images. Compared to current gold standard of sinonasal imaging by MDCT, CBCT provides substantial dose reduction (Guldner et al., 2013). 151

152 Compared to panoramic radiographs, CBCT provides better information about the relationship of the sinus floor to the roots of molars (Jung and Cho, 2012; Shahbazian et al., 2014). Inflammatory diseases of the sinus can be evaluated with CBCT (Ritter et al., 2011). Sinusitis related to apical periodontitis can be identified with CBCT (Lu et al., 2012; Maillet et al., 2011; Shanbhag et al., 2013). However, soft tissue tumors, fluid or blood cannot be differentiated based solely on CBCT (Ritter et al., 2011) Craniofacial Disorders Indications. Compared to traditional dental imaging, CBCT can provide additional information for the treatment planning and complex management of craniofacial disorders and syndromes. CBCT volume renderings allow complete representation of the altered three-dimensional anatomy that is the hallmark of most craniofacial disorders. Additionally, CBCT is useful for evaluating positions and orientations of impacted teeth, extent and involvement of bony structures with palatal or alveolar cleft, and variations of normal bony structures (Kuijpers et al., 2014) Orthodontics. Children and young adolescents, who comprise the substantial majority of patients receiving orthodontic treatment, have increased sensitivity to cancer induction by radiation. Estimates range from at least two times greater sensitivity (NA/NRC, 2006; UNSCEAR, 2013) to 10 times greater than adults (NA/NRC, 2006), depending on the tissue irradiated and the age of the patient. Additionally, most orthodontic CBCT imaging, excluding small volume acquisitions for localizing impacted teeth, involves large fields of view, including structures in the skull base and neck. Thus, it is incumbent on professionals using CBCT to image children and young adolescents to be especially judicious in their use of this imaging modality The recent position paper of the AAOMR presented the following evidence-based guidelines for CBCT use in orthodontics (AAOMR, 2013): image appropriately according to clinical condition; 2. assess the radiation dose risk; 152

153 minimize patient radiation exposure; and 4. maintain professional competency in performing and interpreting CBCT studies These AAOMR guidelines are consistent with the 2012 American Dental Association (ADA) advisory statement regarding the use of CBCT in dentistry and the general principles promulgated in the joint ADA-FDA guidelines (ADA, 2015a; 2015b). However, they are less explicit than the recommendations found in the European SEDENTEXCT report (EC, 2012). The SEDENTEXCT guidelines clearly state that CBCT examinations should not be repeated routinely on a patient without a new risk-benefit assessment having been performed, and that using CBCT for routine or screening imaging is unacceptable practice Recommendation 88. CBCT examinations shall not be used for routine or serial orthodontic imaging Obstructive Sleep Apnea. CBCT can be useful in the management of obstructive sleep apnea. CBCT volumes have been used to assess dimensional and morphologic changes in the upper airway, as well as to assess changes in these parameters after appliance or surgical therapy. While current studies suggest such efficacy of CBCT imaging, further evidence is needed to document its impact on patient outcomes (Alsufyani et al., 2013) Equipment and Facilities The amount of scattered radiation produced when a radiation beam is incident on the human head at a given distance depends on the kilovoltage, milliampere-seconds, and the volume of tissue irradiated. Panoramic dental radiographic units produce relatively little scatter because the beam is only ~3 100 mm at the patient's head. In CBCT systems, the x-ray beam may entirely cover the maxillofacial region and is commonly as large as mm at the patient's head. Scattered radiation exposure at a fixed distance (e.g., 1 m) will be approximately 300 times higher for a CBCT system, compared with a panoramic x-ray system

154 Scattered radiation will increase linearly with the workload, i.e., the total milliampereseconds used per week. Panoramic dental radiography is a well-established imaging modality, and workloads may be reliably estimated from the literature (MacDonald et al., 1983; Reid and MacDonald, 1984; Reid et al., 1993) CBCT, however, is a relatively new imaging modality and its clinical indications continue to expand. It is likely that increased efficacy of CBCT will result in continued increases in its clinical utility. As new indications for appropriate use of CBCT are added, the CBCT workload in dental clinics will increase proportionally Preliminary assessment of the data from the 2015 NEXT Survey (Farris and Spelic, 2015) show proportionately lower exposures for children compared with adults: average milliamperage for children, 6.8 ma, and for adults, 8.3 ma; scan time for children, 7.7 s, and for adults, 12.1 s. The substantial majority of examinations were performed on adults: 11.6 per week versus 1.3 per week for children Although it may be tempting to physically replace a panoramic radiographic device with a CBCT system by simply removing the old unit and installing the CBCT gantry, this method creates the potential for substantial radiation exposure to people in the vicinity of the CBCT system. Some panoramic x-ray units have been installed in dedicated, shielded dental x-ray rooms. It is not uncommon, however, to find panoramic radiographic units installed on an open space within the dental suite, often a remote corner or alcove. The small field size and resultant minimal scatter from panoramic units may permit such installations while maintaining radiation exposures to persons in the vicinity well below permissible levels However, CBCT systems placed in the location formerly occupied by a panoramic dental unit will generate substantially more scattered radiation per exam, and may not result in exposures that are ALARA. The combination of substantially greater volume of tissue irradiated and potentially much higher workload must be considered when assessing radiation safety requirements for a CBCT installation. It is preferable to install a CBCT unit in a dedicated room that meets these safety requirements

155 Using the NEXT data of 11.6 adult CBCT examinations per week and 1.3 pediatric CBCT examinations per week, and assuming a very heavy workload and tripling these exam frequencies, the resulting number of exams would be 45 per week. Even with this estimated weekly workload, the occupational exposure would be well below the regulatory limits for a well-designed CBCT facility. However, for a poorly designed CBCT installation, exposures to the general public, office staff, and occupationally exposed personnel could potentially exceed the respective regulatory maximums. Hence, we recommend an initial radiation shielding design be performed by a qualified expert before installation of a CBCT, and that the qualified expert annually assess the radiation safety of the installation by validating the workload assumptions and recalculating exposures when indicated Radiation Dose Structured Report Equivalent Needed for CBCT Modern medical CT units provide a DICOM radiation dose structured report that allows determination of the patient dose from individual examinations. Differences in acquisition physics and data structures between CBCT and MDCT prevent the same method of determination and require development of a new method of determination for CBCT In addition, there is presently much discussion among medical and health physicists, and radiation biologists, regarding effective dose versus dose area product as a metric for expressing dose and risk to the patient from a particular examination (NCRP, 2012b). In this report, we have elected to use effective dose because it provides units in terms of risk and because the presentation of dose and risk in the dental literature is entirely in terms of effective dose While the use of dose area product (DAP), also known as the Kerma Area Product (P KA ) has been advocated as a measure of dose for CBCT units, their accuracy as a measure of risk for the small volumes acquired for dental diagnostic imaging is debatable (EC, 2012; HPA, 2010). In relating DAP to effective dose, a conversion coefficient must be used. Illustrating this problem, one study using a single CBCT unit calculated conversion coefficients for DAP to effective dose for large to small FOVs and found that a 3.8-fold range of values was required for different field sizes and anatomic locations (Kim et al., 2014). A 7.5-fold range of DAP to effective dose ratios 155

156 were calculated from the adult phantom data in a recent study encompassing a large number of measurements on CBCT devices of varying beam energies (Ludlow et al., 2014). The use of volume height in the place of projection area in this study resulted in statistically improved accuracy in the estimation of effective dose but still led to a range in the conversion coefficient of 2.4-fold for adult phantom imaging. This improvement is intriguing as beam height may be easily substituted for beam area in dose calculations. While use of volume height in place of area in dose calculation warrants further investigation, it is apparent that development of universal conversion coefficients to translate simple measures of exposure to patient dose with the goal of risk estimation is problematic. In addition to Kerma Area Product or dose area product or dose height product (DHP) for different scan parameters, it would be useful for manufacturers to provide machine specific coefficients for the conversion of P KA, DAP or DHP into effective dose so that an estimate of risk associated with an examination would be available for the clinician and patient. Recommendation 89. Manufacturers should develop P KA values for CBCT acquisitions and provide conversion coefficients or other dose metrics necessary for the calculation of effective dose in order to allow an estimate of risk for each acquisition Advantages of Pulsed Systems over Continuous Radiation Exposure Systems Dental radiographic x-ray generators use transformers and other circuits to step-up the 120 volts AC source provided by the utility to the kilovoltage range needed for x-ray imaging. In recent decades, dental radiographic x-ray generators have most often been designed to produce relatively continuous waveforms at a fixed milliamperage. Varying the exposure time is typically used to change the amount of radiation used to expose the patient and create the image. For ease of use and consistency, many generators display different patient sizes (pediatric, small, medium and large adult) so that the operator may select the most appropriate technique Most image receptors used in CBCT applications are unable to record x-ray exposure during the period when the image detector integrates (processes) the x-ray energy absorbed in individual receptor pixels and transfers this signal to the computer. Continued x-ray exposure during signal integration contributes to patient dose but adds nothing to image formation. To eliminate this 156

157 unnecessary patient exposure, many CBCT units utilize a pulsed x-ray source, where x-ray emission is intermittently turned off during the image acquisition process. This feature can significantly reduce patient exposure when appropriately applied and is explicitly engineered into CBCT equipment. For example, a pulsed generator operating at 7 ma for 20 s may deliver substantially <140 mas. This methodology for pulsing the x-ray beam in sequence with active pixel measurement should not be confused with half-wave rectification found in some older dental x-ray machines. Whether an x-ray generator produces continuous or pulsed x-ray beams, it is critical that the total dose be measured by the qualified expert and compared with published benchmarks to assure that patient image quality is optimized and the dose ALARA. The qualified expert should ensure that his/her measuring instrumentation is capable of capturing data from both continuous and pulsed x-ray systems Advantages of 180 Degree Scan versus 360 Degree Scan Some newer CBCT machines have an optional acquisition mode that rotates the x-ray source and detector through a 180 degree arc rather than a 360 degree arc. This reduces the radiation dose by close to 50 % at the expense of a somewhat noisier image. However, an in vitro study on detection of artificially created TMJ bone defects (Yadav et al., 2015) showed no differences in detection efficacy between the two rotational acquisition modalities. If the results of this study are confirmed and are shown to apply to other diagnostic tasks, such as implant site dimensional measurements and precise relationships between mandibular third molar roots and mandibular canals, this could become the technique of choice in some well-defined situations to substantially reduce radiation dose while maintaining diagnostic efficacy Location of Equipment and Requirements for Shielding Requirements for equipment location and shielding for CBCT facilities are based upon CT requirements as promulgated in NCRP Report No. 147 (NCRP, 2004a). There are special considerations for CBCT operation, based on machine location, machine settings, imaging geometry, position of the patient, and workload. These issues are dealt with in general terms in Sections and 4.5.1, and are given in greater detail in Appendix D. 157

158 Administration and Education Administrative and Regulatory Considerations Regulatory, accreditation, and professional organizations provide the oversight and guidance needed to meet accepted image quality standards, safety standards, and standards of care. The requirements of such bodies are accomplished through the practitioner s or facility s quality control program (NCRP, 2010). Operators of radiation-emitting devices such as dental x-ray machines must be familiar with and comply with applicable federal, state, and local regulations Compliance with FDA Medical Device Regulations and Electronic Product Radiation Control Performance Standards The FDA Center for Devices and Radiological Health is responsible for regulating firms who manufacture, repackage, relabel, and-or import medical devices sold in the United States, including dental x-ray unit (http// Overview/default.htm) Legally marketed dental x-ray devices comply with federal regulations for medical devices and radiological health. Under the medical device regulations (21 CFR Subchapter H), dental x- ray devices must be cleared by the FDA before being offered for sale in the United States. These regulations are intended to provide reasonable assurance of safety and effectiveness for medical devices marketed in the United States. To verify that a particular device has been reviewed by the FDA, practitioners can search the FDA s online searchable database for Medical Device Premarket Notifications at http// The radiological health regulations (21 CFR Subchapter J) are intended to protect the public from hazardous or unnecessary radiation exposure from radiation emitting-electronic products. These regulations require that manufacturers of radiation emitting electronic products adhere to specific reporting, recordkeeping, and labeling requirements as well as comply with applicable performance standards in 21 CFR through Diagnostic x-ray devices that 158

159 comply with the radiological health regulations will include certification, identification, and warning labels. These labels will be permanently affixed, legible, and readily accessible to view when the device is fully assembled for use [21 CFR (b) and (a)]. Figure 10.1 shows identification and certification labels A radiation-emitting device that meets the FDA requirements will be deemed cleared by the FDA. It is worth noting that the appropriate terminology uses the word cleared. The FDA does not approve radiation-emitting devices. An FDA cleared device meets the stringent design requirements necessary to minimize the dose to the operator with proper use of the equipment When new technology is introduced, especially in the current global marketplace, it is critical that buyers and operators be certain that the devices they are purchasing and using are cleared by the FDA General Considerations The following are good imaging practices in a dental setting: Clear policies and procedures governing safe and effective use of radiation in the dental practice. For example, quality assurance and quality control (Section 5.2), and radiation safety of the patient and operators (Sections 4.4 and 4.5). 2. Selection criteria for all imaging procedures (see Sections for general radiology and for CBCT). 3. Recording of the date, number, types, retakes, and operator for each examination. 4. Maintenance of all records at least as long as required by the administrative authority, e.g., state dental or medical board, or other government agencies

160 Fig FDA required identification and certification x-ray equipment labels. Top and middle photos show the two labels required for FDA-cleared equipment (indicated by compliance with DHHS Rules 21CFR, subchapter J). Bottom photo shows placement of the two labels on an x-ray tube

161 Hand-Held X-Ray Devices There are several handheld x-ray units for sale in the United States. The design of the internal components of these machines varies tremendously, as do the dose levels and exposure times. FDA s performance standards for intra-oral imaging devices, including hand-held systems are included in sections 21 CFR and These performance standards address requirements such as control and indication of technique factors, reproducibility, and source-toskin distance. Some units offered for sale, primarily through the Internet, have not been cleared by the FDA and present radiation hazards to the operator and the patient (Sections and ) Recommendation 90. Only hand-held dental x-ray devices cleared by FDA for sale in the United States shall be used Some regulatory organizations have implemented rules and regulations preventing the user from holding the x-ray tube. These rules and regulations are unnecessary and impractical for FDA-cleared hand-held x-ray systems. The risks associated with holding the x-ray tube are mitigated by properly designed and labeled hand-held x-ray systems. Because properly designed and labeled hand-held systems can offer a cost-effective, flexible, and safe alternative to wallmounted systems, these rules and regulations should be relaxed for equipment that is designed to be hand-held Recommendation 91. Regulations preventing the user from holding the x-ray unit should not apply to equipment cleared by FDA that is designed to be hand-held CBCT Units FDA s performance standards specific to CT systems are included in 21 CFR Of particular importance to CBCT systems is the requirement to include quality assurance and control information (21 CFR d). CT manufacturers are required to provide an image quality phantom, instructions for using the phantom, and a schedule for its use. 161

162 Considerable variability exists in the way state radiation control programs address CBCT systems, if at all. At the time of this writing, most states do not have specific requirements for dental CBCT systems and consider CBCT to be a form of dental radiography or panoramic radiography, although some states view CBCT to be a form of medical CT. The FDA classifies CBCT systems the same as conventional CT systems. The committee thinks that dental CBCT occupies a unique niche in the imaging world; CBCT should be considered neither a traditional dental equipment (intraoral, cephalometric or panoramic equipment) nor a conventional medical CT system The CRCPD Suggested State Regulations (SSR), Part F (Diagnostic and Interventional X- Ray & Imaging Systems; were revised in 2015 and include specific recommendations for CBCT units. At the time of writing, four states have adopted the SSR and others are considering it Recommendation 92. States shall develop and apply specific regulations for the dental uses of CBCT The radiation safety officer (RSO), which in a typical dental practice is the dentist, is responsible for remaining aware of current and potentially evolving changes in regulatory requirements for CBCT. The qualified expert may provide valuable help in this ongoing process Even in the complete absence of any specific state requirements for CBCT use, the RSO remains responsible for the safe use of radiation at the facility. Hence, it is prudent for the RSO to remain aware of the evolving state of the practice regarding state and local CBCT regulations as well as CBCT quality and safety practices, and to establish procedures in the dental clinic with these in mind. An experienced qualified expert can be a valuable resource in this important ongoing activity and may serve as the RSO

163 Independent of any federal or state regulations, each dental practice employing CBCT should establish and maintain policies and procedures that address at least the following: qualifications (including training and continuing education requirements) of individuals who may perform or read CBCT exams; 2. personnel monitoring of occupational exposure, including periodic review by the radiation safety officer (RSO) or qualified expert; 3. a CBCT quality assurance program, including both equipment related QC and clinically related QA activities; 4. radiation safety and regulatory compliance program; 5. standard CBCT protocols for common clinical indications; and 6. periodic review of CBCT protocols by the dental practitioner and the qualified expert Advanced Diagnostic Imaging Accreditation. The Medicare Improvements for Patients and Providers Act of 2008 requires the accreditation of suppliers of the technical component of advanced diagnostic imaging services in order to obtain payment from the Centers for Medicare and Medicaid Services (CMS). For more information go to the CMS website ( and search for advanced diagnostic imaging accreditation This provision of the act went into effect January 1, 2012, and includes dentists who obtain and bill Medicare for the technical component of CBCT examinations. The accreditation standard applies only to the suppliers of the images themselves, and not to the clinician s interpretation of the images. The purpose of the accreditation is to ensure that quality images are produced in a safe and effective manner that benefits the patient Some states and private payers have adopted similar regulations. Clinicians and imaging facilities that utilized CBCT are advised to consult with local officials or representatives of the individual insurance company or payer for details specific to their location or situation

164 Education and Training NCRP Report No. 127 and Report No.134 (NCRP, 1998; 2000;) and ICRP Publication 113 (ICRP, 2009) recommend that all dental personnel be appropriately trained in radiation protection. Basic familiarity with radiation protection can be expected in those who by education and certification are credentialed to expose radiographs, i.e., dentists, registered dental hygienists, certified dental assistants, and radiologic (or dental radiologic) technologists. Curricula for their education are subject to recommendations by various professional organizations and requirements of accrediting and credentialing agencies (IAC, 2015; ICRP, 2009). These recommendations included credentialing of faculty and adequacy of resources and curricula for predoctoral and postdoctoral education, and required frequency of continuing education. Others have shown that dentists who are better informed in radiation science are more likely to adopt modern dose-optimization technology (Svenson et al., 1997b; 1998) The ability of office personnel to understand and implement all of the recommendations in this Report cannot be assumed. Other personnel, e.g., secretaries, receptionists, laboratory technologists, who are not credentialed for performing radiographic procedures may be subjected to incidental exposure to radiation. These personnel are likely to have received little or no training or experience in radiation protection The required training may be provided by any combination of self-instruction (including reading), group instruction, online instruction, mentoring, or on-the-job training. Periodic evaluation of staff practices will determine the need, if any, for retraining. Essential topics to be covered in the training program include: the ALARA principle; risks related to exposure to radiation and to other hazards in the workplace; dose limits; sources of exposure; basic protective measures; secure access to radiation equipment; 164

165 warning signs, postings, labeling, and alarms; responsibility of each person; overall safety in the workplace; specific facility hazards; special requirements for women of reproductive age; regulatory and licensure requirements; and infection control This training may be expedited by the development and maintenance of a site-specific radiation protection manual Recommendation 93. Radiation safety training shall be provided to all dental staff and other personnel, including secretaries, receptionists, and laboratory technologists. This training shall be commensurate with the individual s risk of exposure from ionizing radiation Recommendation 94. Every person who operates dental x-ray imaging equipment or supervises the use of such equipment shall have current training in the safe and efficacious use of such equipment When new imaging technology is introduced into a dental practice it is essential that the dentist and all operators be properly trained so as to be thoroughly familiar with the safe and efficient operation of the equipment. Continuing education resources are generally available to keep the dentist apprised of new developments Recommendation 95. The dentist should regularly participate in continuing education in all aspects of dental radiology, including radiation protection Recommendation 96. Opportunities should be provided for auxiliary personnel to obtain appropriate continuing education credits. 165

166 Digital Imaging In addition to the basic education and training required for film-based imaging, the operator should be trained in the use of the radiographic imaging software that is used to acquire and manipulate the images. This training should be provided by the manufacturer or vendor of the equipment Furthermore, the operator should be educated and trained in the appropriate quality assurance and quality control protocols to assure the optimal performance of the film or digital imaging equipment components (Sections and 5.2.6) Hand-held Imaging Systems Hand-held dental x-ray units are relatively new to the marketplace and require specific additional education for their safe and efficient operation Practitioner Additional Safety Concerns. Practitioners should be aware of the potential for misuse of hand-held x-ray equipment and assure that the appropriate safeguards are in place. In addition, there is a potential for increased operator radiation exposure if the device is not used properly Operator Training. The hand-held x-ray equipment manufacturer must provide training materials for the operator. A DVD or online source could be used for operator training Operator training materials should include the basics of x-ray production and scatter (some operators such as dental assistants may not have had formal radiation safety training) and information on proper positioning. The positioning information should include the position of the patient, operator, location, and orientation of the hand-held device, and operator s hand positioning on the device. This training should emphasize that the operator be positioned in a way that minimizes their exposure to backscattered radiation. In addition, the value of the x-ray 166

167 shield which is an integral part of the unit should be emphasized, i.e., the shield must always be in place It is critical that operators follow the positioning instructions. Failure to follow proper positioning techniques can result in an increased exposure to backscattered radiation to the operator Recommendation 97. The manufacturer shall provide training pertaining to the safe operation of the hand held unit Qualified Expert Required Information. The primary training issue for the qualified expert is the radiation safety of the hand-held x-ray unit Recommendation 98. The manufacturer of hand-held dental x-ray units shall provide information suitable for the qualified expert regarding radiation leakage, backscatter radiation, and the importance of the integral radiation shield CBCT Imaging Systems CBCT units are an order of magnitude more sophisticated than any of the other dental imaging modalities and they require specific additional education for their safe and efficient operation In addition, the operator should be educated and trained in the appropriate quality control protocols to assure the optimal performance of the digital imaging equipment components (Sections 5.2.5) Training for Practitioners The complexity of CBCT image acquisition, and the subsequent multiplanar demonstration of patient anatomy, are far more complex than any imaging previously employed in dentistry. 167

168 Thus, it is incumbent on practitioners to ensure that they receive proper training in the safe and effective use of this modality and provide opportunity for appropriate levels of training for the staff Recommendation 99. The predoctoral dental curricula shall include didactic and clinical education on physics of CBCT image production, artifacts that can lead to image degradation, indications, and limitations of CBCT in dental practice, and the effects of acquisition parameters on radiation dose Recommendation 100. Postdoctoral or clinical residency curricula shall expand upon the predoctoral education and include discipline-specific indications and limitations of CBCT imaging and the effects of acquisition parameters on radiation dose Recommendation 101. Dental practitioners who own CBCT units or use CBCT data sets in their clinical practice and who have not received CBCT education as part of their predoctoral, postdoctoral, or equivalent to predoctoral education shall acquire equivalent understanding of the basic radiation safety aspects of CBCT imaging and sufficient knowledge in the indications and limitations of CBCT imaging Recommendation 102. Dental personnel who operate CBCT units shall be adequately trained in the proper operation and safety of the units. They should demonstrate adequate knowledge of different protocols affecting the image quality and radiation dose to the patient Inadequate knowledge of the anatomy or not providing a proper interpretation of the image data set would negate and render moot any radiation protection benefits gained from safe and effective image acquisition. Thus, it is critical that the practitioner receive appropriate education and training in the interpretation of the anatomy as displayed on multiplanar and post-processed three-dimensional images

169 Training for Operators. The operators of CBCT equipment are those licensed by the state in which they practice to operate dental radiographic equipment. Operators often select the equipment settings and perform image acquisition. In most states, operators of CBCT equipment are usually dental hygienists or dental assistants Recommendation 103. Prior to working with CBCT equipment, operators shall receive education on the basics of CBCT technology, the risks associated with radiological imaging, and training on the effective operation of CBCT equipment. This education must include principles of CBCT image formation, equipment settings and their impact on patient dose, and common artifacts associated with CBCT images Recommendation 104. All operators shall complete training on each individual CBCT system they will be using, as provided by the manufacturer. This device specific training must include patient positioning, the range of user selectable exam settings, and their effect on dose, protocol selection, image processing options, and periodic maintenance schedules Training for Qualified Experts. To be qualified for evaluation of CBCT equipment an individual must be a qualified expert with a minimum of 3 h CBCT training (available as online training) and have evaluated at least three CBCTs under the supervision of an experienced qualified expert Recommendation 105. A qualified expert shall have appropriate training and mentored experience in the evaluation of dental CBCT facilities prior to functioning independently Continuing Education for Practitioners, Operators, and Qualified Experts. CBCT technology is continually improving and practitioners, operators, and qualified experts must stay up-to-date. Manufacturers may provide software updates that substantially change the operation of the CBCT unit, which may require re-education and re-training of all parties. Similarly, hardware updates, while occurring less frequently, will also require additional education and 169

170 training. It is the responsibility of the dentist to ensure that all office personnel are properly educated and trained in the safe and efficient operation of the equipment Recommendation 106. Every person who operates CBCT equipment, supervises the use of CBCT equipment or tests and evaluates the functions of CBCT equipment shall have ongoing continuing education in the safe and effective use of that equipment

171 Summary and Conclusions Oral and maxillofacial radiology encompasses a wide variety of techniques, ranging from traditional intraoral, panoramic and cephalometric imaging to more recently introduced digital, hand-held, and CBCT imaging While significant advances have been made in radiation dose reduction to patients and the public, there are still many examples of the utilization of equipment, supplies, and applications that are outdated and inappropriate Attention must be paid not only to how a radiographic image is captured but also to when the image should be captured. The dental clinician can minimize the exposure to the patient while maintaining diagnostic yield by utilizing the following: selection criteria have a good reason for acquiring any image; 2. fastest available image receptor; 3. optimized exposure technical factors; 4. rectangular collimation with intraoral imaging; 5. thyroid shielding for all intraoral images, and for other examinations as appropriate; 6. smallest FOV and lowest dose acquisition parameters commensurate with the diagnostic task in CBCT; 7. continuous quality control programs for equipment, techniques, film processing, and image receptors; and 8. up-to-date training for all personnel Dentists who conduct their radiology practices in accordance with the requirements and suggestions in this Report can obtain maximum benefit to the oral health of their patients and minimum radiation exposure to patients, operators, and the public. All of the factors addressed in this Report are important and interrelated; quality practice dictates that no shall statement be neglected and that should statements be incorporated whenever possible. The technical factors, including office design and shielding, equipment design, clinical techniques, image receptors, 171

172 darkroom procedures, quality control, and quality assurance are essential. However, the professional skill and judgment of the dentist in prescribing radiologic examinations and interpreting the results are paramount While radiogenic harm due to most very low-dose dental x-ray examinations may not be unequivocally demonstrable, recent epidemiological studies have shown an association between low-dose exposures associated with CBCT (doses on the order of those found with MDCT) and increased cancer risk across the population (Appendix I) Given the uncertainty regarding the estimated risk from low-doses such as those found in diagnostic imaging (NCRP, 2010b; UNSCEAR, 2012), there is disagreement about the application of the risk estimates to policy development and radiation protection issues (AAPM, 2012; HPS, 2016). However, given the large number of dental images taken annually, the possibility that the risks are real, especially for CBCT imaging, demands that they be taken seriously in the interest of patient, staff, and public safety

173 4115 Appendix A Quality Control for Film Processing Radiation exposure to the patient, operator, and public can be reduced by minimizing the need for repeat exposures because of inadequate image quality (NRPB, 2001). In addition, the chemical solutions must be maintained at the proper activity level. As the chemicals are depleted or oxidized, the films will be lighter resulting in an increased exposure times and higher doses to the patients and staff. Film processing chemistry and procedures, image receptor performance characteristics, and darkroom integrity must be evaluated at appropriate intervals. These routine quality control procedures can be performed by dental office staff A.1 Five Basic Rules for Film Processing Films should be processed at the time and temperature specified by the film manufacturer. Film processing is a chemical reaction requiring accurate control of the processing time and temperature. An important part of processor quality control is maintaining the appropriate developer and fixer activity. This is accomplished through replenishing of the solutions in the developer and fixer tanks. 2. The developer and fixer must be replenished regularly to maintain diagnostic image quality, and minimize patient dose. Eight ounces of replenisher should be added every day, assuming 30 intraoral or five panoramic films. An additional eight ounces of replenisher should be added per day for each additional 30 intraoral or five panoramic films processed (White and Pharoah, 2014). Manufacturer s instructions should be followed where applicable. 3. Never top off the chemical tanks with water. This dilutes the chemicals, reduces image quality, and could lead to an increase in patient radiation dose

174 Developer and fixer solutions should be changed every two weeks. Over time the solutions tend to collect bits of debris from the film, become depleted, and oxidize. Consequently, it is necessary to drain the solutions, clean the tanks, and fill the tanks with fresh chemicals. 5. The water in the wash tank should be changed daily for up to 30 films developed per day. For higher volumes, the water should be changed after every 30 films. (Some processors have water flowing through the wash tanks the water in these processors does not have to be changed due to the continuous flow of fresh water.) Improper washing of films will result in premature fading and staining of the images A.2 Quality Control A.2.1 Sensitometry and Densitometry The most sensitive and rigorous method of quality control requires the use of a sensitometer, a precise optical device to expose a film to produce a defined pattern of optical densities in the processed film. These densities are then measured with a densitometer, and compared to the densities of a similarly exposed film previously processed in fresh solutions under ideal conditions. These values are placed on a control chart. Any change beyond pre-specified limits indicates a problem with processing which could be a result of changes in development time or temperature, or due to depleted or contaminated solutions. This method requires additional equipment but only a few minutes of operator time to execute. It is highly recommended for the busy facility, but simpler, less costly methods may be adequate for average dental offices A.2.2 Dental Radiographic Quality Control Two devices are available from most dental supply companies for simple quality control of film processors a dental radiographic quality control device (DRQCD) and an aluminum step wedge. In addition to daily QC, the DRQCD assists in selecting appropriate exposure time to 3 Gray, JE (2015). Personal Communication. (DIQUAD, LLC, Steger Illinois) 174

175 assure that patients are receiving an appropriate radiation dose. A third test device can be constructed from the leaf foils in dental film packets A Dental Radiographic Quality Control Device. This device consists of a small sheet of copper and a comparison optical density step wedge. For quality control, an exposure is made with a film packet under the copper, the film is processed, and then compared to the step wedge. If the film density changes by more than one step then a change in photographic processing has occurred and it will be necessary to determine and correct the cause This device is also useful in establishing the appropriate exposure time for dental radiographs. In this case, a film packet is exposed under the copper plate and compared to the optical density step wedge. The appropriate exposure time results in the film density matching the middle step of the step wedge A Aluminum Step Wedge. An aluminum step wedge with 1 mm steps can be used for film processor quality control. A film packet is exposure under the aluminum step wedge and the film is processed with fresh film processing chemistry. This film becomes the comparison or baseline film. For daily quality control purposes, the procedure is repeated with the resultant film being compared to the baseline film. If the steps of the baseline film and the recently exposed film are not similar then it will be necessary to determine and correct the cause A Lead Foil Step Wedge. A step wedge can be made of multiple layers of the lead foil from dental film packets (Valachovic et al., 1981). Overall size of the stepwedge should be similar to that of a standard intraoral film. It is made to resemble stairs. There should be at least six steps The lead foil step wedge is used in the same manner as the aluminum step wedge A Reference Film. Use of a properly exposed and processed intraoral film as a reference has been proposed as another method of quality assurance (Valachovic et al., 1981). When using this method, a high-quality film is attached to a corner of the view box. Subsequent clinical films can then be compared with this reference film. This method is not as sensitive or reliable as the 175

176 use of the DRQCD device, or a stepwedge, and is not recommended for routine use. In rare circumstances it may be used as a stopgap measure, usually in facilities with very low radiographic workload (fewer than 10 intraoral films per week)

177 4210 Appendix B Quality Control for Digital Imaging Systems B.1 Quality Control of Digital Intraoral Systems Quality control testing of digital systems requires: computer display adjusted to display a high-quality radiographic image and viewed under optimal conditions; 2. suitable phantom or test object to be used for the assessment of image quality; 3. procedure providing verification that the radiographic technique being used yields the maximum diagnostic information at an acceptable level of dose (optimization); 4. exposure of a baseline image to serve as a reference for subsequent images; 5. exposure of follow-up radiographs at regular intervals; and 6. system of record keeping for purposes of documentation B.1.1 The Display Since digital radiographs are viewed on a computer display, it should be verified that the display is viewed under optimal conditions. The display should be tested to verify that it is functioning optimally and the brightness and contrast are properly adjusted Digital radiographs should be viewed with the center of the display positioned slightly below eye level. Subdued lighting should be used and every effort should be made to eliminate reflections from extraneous sources of light such as room lights or view boxes The display should be checked periodically using the Society for Motion Picture and Television Engineers (SMPTE) Medical Diagnostic Imaging Test Pattern or the equivalent. The overall image should be inspected to insure the absence of gross artifacts such as blurring or bleeding of bright display areas into dark areas. All the provided gray levels should be visible 177

178 and both the 5 % and the 95 % areas should be seen as distinct from the surrounding 0 % and 100 % areas. Brightness and contrast should be adjusted until these conditions are met (Gray, 1992; Gray et al., 1985) B.1.2 Quality Control Phantoms A thorough evaluation of image quality requires a phantom containing suitable test objects for assessing low-contrast detectability and spatial resolution as well as a step wedge or some other suitable object covering the relevant range of radiographic attenuation (Mah, 2011; Udupa, 2013). The phantom should be exposed using the source-to-image distance used clinically and the test objects should be positioned at the same distance from the x-ray source and image receptor as the relevant anatomy B.1.3 Baseline Exposure Assessment The object of the original baseline assessment is to evaluate the technique being used for routine exposures and to improve on it, if possible. The objective is to determine the lowest exposure at which the greatest number of low-contrast details are visualized and the highest resolution is obtained while continuing to display the full range of clinically relevant gray levels. Established guidelines for Diagnostic Reference Level and Achievable Dose set limits on the exposures that should be used, even when the image receptor is capable of producing high quality images at levels of radiation exposure exceeding these guidelines. NCRP 172 establishes the DRL and AD for intraoral imaging at 1.6 and 1.2 mgy, respectively (NCRP, 2012b) A starting point for baseline exposure assessment can be obtained from Table 6.1 of this report. This phase is a process of trial and error but it is a necessary step before quality control monitoring begins

179 4269 B.1.4 Baseline Image Once the baseline exposure time is established, the test image should be saved for future reference. Any information extracted from the image, as well as the geometry and exposure factors should be recorded A new baseline exposure assessment should be performed and a new baseline image acquired if any components of the x-ray equipment are altered, repaired, or adjusted, or if any changes are made to the hardware or software used for image capture B.1.5 Follow-up Images Following the baseline assessment, the phantom should be radiographed at regular intervals using the standard exposure geometry and baseline exposure factors. The image should be compared to the baseline image. A significant deviation from the baseline indicates that a change has occurred that should be investigated. Corrective action should be taken as needed. The test should also be performed if damage to the image receptor is suspected after an event such as dropping the image receptor, biting the image receptor, running over the cord with chairs or equipment, snagging the electrical cord, etc B.1.6 Record Keeping A permanent record should be kept of baseline and follow-up data. The date of the test and the name of the person performing the test procedure should be included. The nominal kilovoltage and milliamperage as well as the baseline exposure time should be noted as well as the technical factors that are measured. A separate log should be maintained for every x-ray unit and image receptor combination and, in the case of a practice using PSP plates, every x-ray unit and scanner combination. The following is a quality control record containing the essential elements discussed above:

180 4299 Quality Control Record Image receptor (Manufacturer, Model, Serial #) X-ray Machine (Manufacturer, Model, Serial #) kvp ma Baseline Quality Control Exposure. sec 4310 Baseline Date Name Steps Line-Pairs Top Row of Contrast Holes Second Row of Contrast Holes Date Name Steps Line-Pairs Top Row Of Contrast Holes Second Row of Contrast Holes

181 4315 Appendix C Historical Aspects of Digital Imaging The benefits to the practice of dentistry from capturing skiagrams, as x-ray images were called at the time, were realized soon after the discovery of x rays. During the following 100 y substantial technological improvements advanced most aspects of radiological imaging; however, the film based format of radiographic image capture, display, and archiving remained largely unchanged throughout most of the 20th century. Xeroradiography, with its capture of image detail, was a somewhat viable alternative to film based methods; however, initial investment cost, unique equipment requirements, and perhaps a reluctance of radiologists to interpret a blue radiographic image on dull white paper likely played a role in the mainstay of radiographic film into the 21st century. Digital imaging has been a facet of general radiological practice since the 1980s, first with computed radiography (using PSP technology) and later with direct digital radiography in various forms (although one can argue that computed tomography was actually the first digital oriented radiological imaging procedure based on the digital acquisition and computational nature of this modality). Recent technological advances have allowed x-ray imaging in the dental practice to quickly embrace digital technology Digital based x-ray imaging for dental applications has been a part of clinical practice since the early 1990s. There are likely a number of reasons for the increase in the number of dental practices that have switched to digital imaging for intraoral and extraoral modalities. A recent study found that 87 % (n = 81) of facilities in the United States are now using digital imaging for intraoral examinations (Farris and Spelic, 2015). A second study in the United States found that 85.8 % (n = 1,312) for facilities are using digital intraoral imaging. 4 This same study found that the percentage of facilities using digital intraoral imaging in the United States was increasing by ~8 % y 1 from 2010 through Another study conducted recently of dental practices in New Zealand found that the majority of dental practices had implemented digital x-ray imaging, and not surprisingly, younger practitioners were more likely to be using digital imaging. Among the 4 Gray, J.E. (2015) Personal communication (DIQUAD, LLC, Steger, Illinois). 181

182 reasons that dental practices preferred digital imaging were the chemical free imaging process, lower dose that digital imaging could offer, the rapid availability of the image, and the ability to digitally archive patient imaging records. Practices surveyed that were still using film tended to be satisfied with the modality and felt that switching to digital imaging would be costly. One survey finding that supports the assumption that digital imaging is a more timely modality than film was the finding that practices using digital imaging tended on average to acquire more images per day Digital imaging first became available for dentistry in the late 1980s when technology was sufficient to allow the digital image capture devices to be packaged suitably for dental applications. In 1987 the French company Trophy introduced their product, RadioVisioGraphy, as a digital based tool for dental x-ray imaging. Although early digital technologies were not capable of the high spatial detail that traditional film provides, these technologies continued to mature, and some device manufacturers now offer a wireless means of image capture. One study demonstrated that 2D imaging with digital technology for bone lesions provided better clinical performance than traditional film imaging. Today the digital technologies for oral radiography fall into two broad categories of image receptors: solid state (predominantly CCD or CMOS based) devices and photostimulable storage phosphor (PSP) technology Although the spatial resolution of digital systems may be inferior to film, the contrast resolution, i.e., the ability to see small density differences, is better for digital imaging (Figure C.1) Similar to imaging equipment available for general radiological imaging, digital based x-ray equipment generally is either PSP based or solid state receptor based. While the fundamental technologies of these two equipment types are different, there are a number of common benefits that these two systems offer

183 Fig. C.1. (Left) film image; (right) digital image. Low contrast area on the digital image (red arrow) is not visible on the film image. Low contrast area consists of 1 mm aluminum disk with a circular hole in two layers of tape

184 One benefit to embracing digital imaging in clinical practice is the elimination of chemical film processing. Film processing can be a time consuming and laborious aspect of x-ray imaging to maintain at an acceptable level of quality. A survey of dental facilities in 2014 ( showed broad ranges for clinical image quality including film background optical density, film contrast, and the quality of film processing. Poor film processing (generally considered to be the under-development of film) can affect clinical image quality and also leads to higher patient doses to compensate. The same 2014 survey found that even for those surveyed sites using D-speed film, patient exposures varied broadly, with the first and third quartiles for patient exposure differing by a factor of 2.3 and 45 % failed an acceptance criteria of 2.6 mgy, i.e., exceeded this radiation exposure level. (The range of exposures for D- speed film was from 50 to 800 mr.) Although arguably PSP based systems still require digital image processing, the general need to provide a darkroom environment for handling film and maintaining a chemical based processing environment are eliminated. Digital images can be easily and quickly transferred to other clinical practices as DICOM standard formatted images using the Internet Likely one of the most substantial benefits of capturing radiographs using digital technology is the ability to conduct digital image processing. Although (intraoral) dental film offers tremendous spatial resolution of 20 c mm 1 or greater, digital image processing can provide a system of tools that offer the clinician the ability to manipulate the image to suit the clinical task at hand. In general the near instant availability of digital images provides a level of convenience for both the dental practitioner and the patient. However, when considering a migration to digital based imaging, clinical considerations are helpful in determining the particular system requirements that are suitable for the practice, such as the routine imaging of challenging anatomical presentations, and the workload for pediatric exams

185 4410 Appendix D Shielding Design for Dental Facilities NCRP Report No. 147 entitled, Structural Shielding Design for Medical X-Ray Imaging Facilities (NCRP, 2004), discusses shielding design for x-ray sources with operating potentials in the range from 25 to 150 kvp. Techniques used for calculating shielding barriers for diagnostic medical x-rays also have been discussed in the literature (Dixon and Simpkin, 1998; Simpkin and Dixon, 1998). Since dental radiography uses equipment similar in radiation quality to that used in diagnostic medical x-ray facilities, this appendix will provide information regarding the unique features of dental radiography equipment so that the qualified expert will be able to design shielding using the methodology described in NCRP Report No. 147 (NCRP, 2004) Conventional building materials in partitions, floors, and ceilings may provide adequate radiation shielding for dental installations. However, assuming that conventional or pre-existing barriers provide sufficient shielding without a qualified expert performing a careful review of the required shielding based on current equipment, current workloads, and occupancy of surrounding areas can lead to exceeding permissible levels of radiation exposure in public and controlled areas, and therefore is ill advised Implementing several of the recommendations of this report (e.g., eliminating the use of D- speed film, using digital imaging, and using rectangular collimators for intraoral imaging) may decrease the total amount of amount scattered radiation produced for each intraoral radiographic image. Diagnostic quality images may be produced using a lower radiation exposure for each image with photostimulable phosphor or direct digital imaging receptors instead of film for intraoral imaging. Whether converting to F-speed film or digital image receptors, where such technique factor reductions are implemented clinically, the attenuation requirements for structural shielding will be proportionally reduced if the total number of exams remains unchanged

186 Despite the common misconception that CBCT systems are nothing more than fancy panoramic x-ray systems and no shielding is needed, scattered radiation from CBCT is substantially higher than from panoramic x-ray systems, typically by approximately a factor of 10 times or more. Compared with panoramic x-ray installations, the substantially higher scattered radiation levels in CBCT installations require significantly greater shielding to maintain radiation exposures to nearby persons ALARA. Because CBCT systems are often replace existing panoramic systems, it is especially critical to have a qualified expert assess the adequacy of shielding prior to the CBCT installation. While some panoramic x-ray systems can be operated in a corridor or alcove without exceeding permissible radiation levels to nearby individuals, CBCT systems installed in a corridor or alcove will often expose nearby persons to doses that exceed permissible levels. Typically, CBCT systems should be installed in an enclosed room, with the thickness of shielding materials determined by a qualified expert. Figure D.1 depicts typical configurations for CBCT systems D.1 General Shielding Principles In dental radiology, the beam energy is determined by the demands of radiographic contrast, but typically ranges from 60 to 70 kvp for intraoral dental radiography. Recently manufactured dental intraoral radiography units do not exceed 80 kvp. [Most intraoral dental units utilize fixed kilovoltage (70 kvp) and fixed milliamperage.] Panoramic x-ray units operate from 70 to 100 kvp. Cephalometric systems are similar to standard radiographic systems and operate from 60 to 90 kvp. Cone beam computed tomography (CBCT) systems generate significant higher levels of scattered radiation since the entire image receptor is irradiated continuously during the exposure, as opposed to irradiation from a small slit aperture in panoramic imaging. CBCT systems operate from 70 to 120 kvp

187 Fig. D.1. Diagram illustrating primary barrier B, protecting person at C from useful beam at a distance d P from dental x-ray source A

188 4479 D.2 Shielding for Primary and Secondary Radiation The primary beam is the intense, collimated radiation field that emanates from the x-ray tube focal spot and tube port, and is incident upon the patient. Figure D.1 illustrates a primary protective barrier B in the useful beam that attenuates the beam before it reaches a person located at C. In most situations, the primary beam also is attenuated by the patient before impinging on the primary barrier. The theory of shielding primary radiation from diagnostic x-ray facilities has been discussed by Dixon and Simpkin (1998) and in NCRP Report No. 147 (NCRP, 2004a) Experimental evidence using the Rando phantom (de Haan and van Aken,1990) suggests that the intensity of the primary beam exiting the patient may be approximately twice that of the scattered radiation (Figure D.2). However, additional attenuation from the image receptor and bony anatomy of the human head, coupled with the relatively small beam size and logistical aspects of intraoral imaging 5 serve to mitigate the primary beam effect. In addition, Figure 7.2 indicates that the radiation exposure exiting the patient is ~0.5 to 1.0 mr for D-speed intraoral x- ray film. (The image in Figure 7.2 was produced using a 400-speed screen-film system which requires ~0.5 mr to produce an optical density of 1.00 on the film.) Entrance exposures are even lower for digital imaging systems so the exit exposure from the patient would be approximately one-quarter to one-half of that with D-speed film. [The recent NEXT survey found that 87 % of facilities in the United States are now using digital imaging (Farris and Spelic, 2015)] Neglecting the primary beam in shielding calculations for dental facilities will not affect the calculated barrier thicknesses or resultant exposures to persons who occupy areas nearby the intraoral radiographic installation Consequently, the NCRP recommends that primary radiation can be neglected in dental imaging. Only scattered radiation must be considered in shielding design for dental facilities Unlike conventional radiology, the primary beam in dental imaging is placed at different locations and angles for intraoral radiography for each image. This results in the radiation being at projected at multiple locations on barrier B in Figure D

189 a Proposed CBCT b. Proposed CBCT 189

190 c Fig. D.2. (a) Initially proposed installation of CBCT system, to replace existing panoramic unit. This installation provides suboptimal radiation protection and would require administrative occupancy restrictions in the hallway during x-ray exposure. (b, c) Options for preferred installation of CBCT system in a different area of the suite, providing significant improvement in radiation protection and eliminating the need for administrative controls on hallway occupancy during x-ray exposure needed for the initially proposed installation

191 D.3 Shielding Principles Shielding design goals for dental x-ray sources are practical values that result in the respective limits for effective dose in a year to workers and the public not being exceeded, when combined with conservatively safe assumptions in the structural shielding design calculations (NCRP, 2004). The shielding design goal is expressed as a weekly value, consistent with workload and occupancy factor data D.4 Occupancy Factors, Use Factors, and Workloads D.4.1 Occupancy Factors Suggested occupancy factors are provided in Table D D.4.2 Use Factors Since one need consider only scattered radiation for shielding design in dental radiography, the use factor is not applicable D.4.3 Workloads Suggested workloads for intraoral (IO) imaging are provided in Table D Suggest workloads for panoramic, cephalometric, and CBCT imaging are given in Table D.3 (see also MacDonald et al., 1983; Reid and MacDonald, 1984; Reid et al., 1993)

192 TABLE D.1 Suggested occupancy factors a (for use as a guide in planning shielding where other occupancy data are not available) (NCRP, 2004). Location Administrative or clerical offices; laboratories, pharmacies and other work areas fully occupied by an individual; receptionist area, attended waiting rooms, children s indoor play areas, adjacent x-ray rooms, reading area, nurse s stations, x- ray control rooms Occupancy Factor (T) 1 Patient examination and treatment rooms 1/2 Corridors, patient rooms, employee lounges, staff toilets 1/5 Public toilets, unattended vending areas, storage rooms, outer areas with seating, unattended waiting rooms, patient holding areas Outdoor areas with only transient pedestrian or vehicular traffic, unattended parking lots, vehicular drop off areas (unattended), attics, stairways, unattended elevators, janitor s closets 1/20 1/40 a When using a low occupancy factor for a room immediately adjacent to an x-ray room, care should be taken to also consider the areas further removed from the x-ray room that may have significantly higher occupancy factors and may, therefore, be more important in shielding design despite the larger distances involved

193 4582 TABLE D.2 Suggested workloads for intraoral (IO) units. Type of Unit Images w -1 kvp mas per Image Film or Image Receptor Speed Low Volume IO F or Digital Medium Volume IO F or Digital High Volume IO F or Digital

194 TABLE D.3 Suggested workloads and technique factors for cephalometric, panoramic, and CBCT examinations. Panoramic Cephalometric CBCT Low volume facility (exams w -1 ) Medium volume facility (exams w -1 ) High volume facility (exams w -1 ) <15 <10 < >30 >20 >20 kvp mas per image for 400-speed film or digital image receptor Slot beam. Depends on pulsed or nonpulsed beam, pulse width, and patient size. 7 Depends on pulsed or nonpulsed beam, pulse width, field of view, resolution, and patient size. 194

195 4588 D.5 Summary Shielding in dental radiography facilities is not as complex as for medical facilities. However, sufficient consideration must be given to future workloads to assure that shielding is adequate. Particularly for new construction and typical circumstances, appropriate shielding adds little to the cost of construction. Prior to facility operation, a performance assessment by a qualified expert is necessary to confirm that occupational and public effective dose limits will not be exceeded. The recommendations in this Report are to be applied to upgraded or new shielding designs, but not necessarily to existing barriers that otherwise met prior requirements

196 4599 Appendix E Dosimetry, Intraoral and Panoramic Imaging E.1 Patient Dosimetry Dental radiographic procedures are very common but the associated x-ray doses are quite low. Application of the ALARA principle to reduction of these doses is justified. For intraoral radiography, changing from D- to E-F-speed film or to digital image receptors results in dose reduction by factors of at least two. Introduction of rectangular collimation to replace the 7-cm round beam reduces dose by factors of four to five. Both of these are accomplished at little or no cost, and together may result in ten-fold reductions in effective doses This Section provides the dentist with data, e.g., Tables E.1 and E.2, on the magnitude of effective doses from typical dental x-ray procedures. General statements are given in this Section that can be used to inform the patient about the radiation doses from dental x- ray procedures and the nature of risk associated with these doses. Additional background on radiation risk assessment is found in Appendix I. Dentists are encouraged to use this information to educate their patients as opportunity provides Tables E.1 and E.2 are taken from literature reporting 2007 ICRP calculations of effective dose Figure E.1 shows the distribution of absorbed radiation doses throughout structures in the maxillofacial region following a full mouth series (Gibbs et al., 1987). While this is an old figure using D-speed film, it is the only such figure in the literature. The doses for E-F-speed film or digital imaging would be approximately one-half of the printed values

197 4629 TABLE E.1 Effective dose of dental panoramic radiography units. Unit Manufacturer kvp ma Time (s) Effective Dose (µsv) Reference Veraviewepocs 3De Morita Al-Okshi (2013) ProMax 3D Planmeca Al-Okshi (2013) ProMax Planmeca Al-Okshi (2013) OP200 Instrumentarium Han (2013) Orthophos CD Sirona Han (2013) Orthophos XG plus Sirona Han (2013) ProMax Planmeca Grünheid T (2012) OP100 Instrumentarium Ludlow (2011) Orthophos XG Sirona Ludlow (2011) ProMax Planmeca Ludlow (2011) Kodak Carestream Ludlow (2011) SCANORA 3D Soredex Ludlow (2011) OP 200 VT Instrumentarium Ludlow (2011) Average Standard deviation

198 4630 TABLE E.2 Effective Doses for plain dental radiographic views. Technique Effective Dose (µsv) FMX with D Speed film and Round Cone 388 FMX with PSP or F-Speed film and Round Cone 171 FMX with PSP or F-Speed film and Rectangular Collimation 35 BWs with PSP or F-Speed film and Rectangular Collimation 5 PA Cephalometric - PSP 5.1 Lateral Cephalometric - PSP

199 Fig. E.1. Isodose curves calculated for full-mouth intraoral examinations obtained at 80 kvp using optimum exposures for D-speed film. Lines without numeric annotations indicate skin surface and internal hard tissue surfaces. Numeric annotations indicate absorbed dose in microgray (1,000 µgy = 1 mgy). For example, the tissues contained within the contour labeled 5,000 receive an absorbed dose of at least 5 mgy (5,000 µgy). (A) Transverse section through the occlusal plane, 7 cm round beams. Note that the teeth receive absorbed doses of at least 12 mgy, and all tissues anterior to the cervical spine receive at least 5 mgy. (B) Same plane with rectangular collimation. Areas contained within each isodose contour are smaller than in A. Absorbed dose is generally confined to the facial area, with posterior regions receiving absorbed doses no >1 mgy (Gibbs et al., 1987)

200 4658 E.2 Operator Dosimetry Figure E.2 provides the supporting evidence for recommendation that the operator exposing intraoral images should stand at an angle of 90 to 135 degrees from the central ray (Figure 4.1)

201 Fig. E.2. Operator exposure as a function of position in a room relative to patient and primary beam for intraoral imaging. View from above for a left molar bitewing. The heavy line in the polar coordinate plot indicates dose by its distance from the center of the plot. Maximum dose is in the exit beam on the side of the patient opposite the x-ray tube. The recommended positions for minimum exposures (crosses) are at 45 degrees from the exit beam. Note that most scattered radiation is backward toward the x-ray tube (de Haan and van Aken, 1990)

202 4685 Appendix F Dosimetry for Multidetector-Multislice Imaging of Dentomaxillofacial Areas TABLE F.1 Effective dose from MDCT scanning of dental and maxillofacial areas. Unit Exam kvp ma Time (s) Voxel (mm) Height (cm) Effective Dose (µsv) Somatom Emotion 6 - low dose (Jeong, 2012) Mandible Somatom Sensation 10 (Jeong, 2012) Mandible Somatom VolumeZoom 4 (Loubele, 2009) Mandible Somatom Sensation 16 (Loubele, 2009) Mandible Mx8000 IDT (Loubele, 2009) Mandible Somatom 64 - low dose (Ludlow, 2008) Jaws Somatom 64 (Ludlow, 2008) Jaws Somatom VolumeZoom 4 (Loubele, 2009) Head ,110 Somatom Sensation 16 (Loubele, 2009) Head Mx8000 IDT (Loubele, 2009) Head ,

203 TABLE F.2 Summary of effective doses from MDCT scanning of dental and maxillofacial areas. MDCT - Isotropic Voxels Average Effective Dose (µsv) Low (µsv) High (µsv) Mandible Jaws Head 1, ,

204 4695 Appendix G Dosimetry for Dental Cone Beam CT Imaging The effective dose data in Tables G1 through G6 as well as the salivary gland, thyroid gland, and brain components of effective dose (recorded without weighting as equivalent dose) were assessed using one-way ANOVA (Tables G7 to G11), followed by pairwise comparisons when appropriate (Tukey HSD)

205 TABLE G.1 Effective doses for standard or default exposures for large FOV CBCT units (>15 cm height). Unit Name (reference) Manufacturer FOV Size H W a (cm) kvp mas Effective Dose (µsv) 3D exam (Rottke, 2013) 3D exam (Schilling, 2013) CB Mercuray (Librizzi, 2011; Jadu, 2010) CB Mercuray (Ludlow, 2008; Jadu 2010) CS 9500 (Ludlow, 2011; Pauwels, 2012; Rottke, 2013) DCT PRO (Qu, 2012a) i-cat FLX (Ludlow, 2013) i-cat NG (Davies, Grunheid, 2012; Ludlow, 2008; Morant, 2013; Roberts, 2009) Iluma Elite (Ludlow, 2008) NewTom 3G (Ludlow, 2008) NewTom 9000 (Qu, 2012b) SkyView (Pauwels, 2012) ProMax Mid stitched (Ludlow, 2015) Imaging Sciences Imaging Sciences Hitachi b c Hitachi b c Carestream c VATECH Imaging Sciences Imaging Sciences c Imtec Cefla b Cefla b 110 automatic 95 Cefla b Planmeca a H W = height x width. b Spherical field of view. c Extrapolated or averaged dose. 205

206 TABLE G.2 Effective doses for standard or default exposures for medium FOV CBCT units (10 to 15 cm height). Unit Name (reference) Manufacturer FOV Size H W a (cm) kvp mas Effective Dose (µsv) 3D Accuitomo 170 (Theodorakou, 2012; Ludlow, 2015) 3D Accuitomo 170 (Theodorakou, 2012; Ludlow, 2015) 3D Accuitomo 170 (Ludlow, 2015) 3D exam (Schilling, 2014) CB Mercuray (Jadu, 2010; Ludlow, 2008; Librizzi, 2011) CB Mercuray (Lukat, 2013) CS 9300 (Ludlow, 2015) CS 9300 (Ludlow, 2015) CS 9300 (Ludlow, 2015) CS 9500 (Ludlow, 2011) DCT PRO (Qu, 2012a) Galileos Comfort (Ludlow, 2008; Pauwels, 2012) i-cat Classic (Ludlow, 2008) J Morita J Morita J Morita Imaging Sciences Hitachi b Hitachi b Carestream Carestream Carestream Carestream VATECH Sirona b c Imaging Sciences i-cat FLX Imaging Sciences

207 (Ludlow, 2013) i-cat FLX (Ludlow, 2013) i-cat NG (Morant, 2013) i-cat NG (Morant, 2013) i-cat NG (Davies, 2012; Ludlow, 2008; Morant, 2013; Pauwels, 2012; Roberts, 2009; Theodorakou, 2012) Iluma Elite (Pauwels, 2012) NewTom VG (Pauwels, 2012) NewTom VG (Theodorakou, 2012) NewTom VGi (Pauwels, 2012; Ludlow, 2012) Imaging Sciences Imaging Sciences Imaging Sciences Imaging Sciences Imtec QR, Verona Cefla auto 81 QR, Verona c OP300 Maxio Instumentarium Scanora 3D (Pauwels, 2012) Soredex a H W = height width. b Spherical field of view. c Extrapolated or averaged dose

208 4719 TABLE G.3 Effective doses for standard or default exposures for dento-alveolar centered small FOV CBCT units (<10 cm height). Unit Name Manufacturer FOV Size H W a (cm) kvp mas Effective Dose (µsv) Reference 3D exam Kavo b Schilling (2013) 3D exam Kavo Schilling (2013) i-cat FLX Imaging Sciences Ludlow (2013) i-cat FLX Imaging Sciences Ludlow (2013) i-cat FLX Imaging Sciences Ludlow (2013) i-cat NG Imaging Sciences Grunheid (2012) i-cat NG Imaging Sciences Morant (2013) Kodak 9500 Carestream Pauwels (2012) NewTom VGi QR, Verona b Pauwels (2012) Prexion 3D TeraRecon Ludlow (2008) ProMax 3D Planmeca b Suomalainen (2009); Ludlow (2008) Promax 3D-upgraded filtration Planmeca b Pauwels (2012); Theodorakou (2012)

209 a H W = height width. b Extrapolated or averaged dose

210 TABLE G.4 Effective doses for standard or default exposures for small FOV CBCT units (<10 cm height) maxillary views. Unit Name Mfg. FOV Size H W a (cm) Region of Interest kvp mas Effective Dose (µsv) Reference 3D Accuitomo 170 J Morita 5 10 Maxilla Pauwels (2012) 3D Accuitomo 170 J Morita 5 14 Maxilla Theodorakou (2012) 3D exam Kavo 4 16 Maxilla Schilling (2013) CB Mercuray Hitachi 10 b Maxilla Jadu (2010) i-cat FLX Imaging Sciences 6 16 Maxilla Ludlow (2013) i-cat NG Imaging Sciences 6 16 Maxilla c Davies (2012; Morant (2013); Pauwels (2012); Roberts (2009); Theodorakou (2012) Pan exam Plus 3D Kavo 6 4 Maxilla Schilling (2013) Pan exam Plus 3D Kavo 6 8 Maxilla Schilling (2013) Promax 3D-upgraded filtration Planmeca 5 8 Maxilla c Qu (2010) Scanora 3D Soredex Maxilla Pauwels (2012) 3D Accuitomo 170 J Morita 4 4 Maxillary anterior Theodorakou (2012) 210

211 CS 9000 Carestream 4 5 Maxillary anterior PaX-Uni3D VATECH 5 5 Maxillary anterior Pauwels (2012) Pauwels (2012) Promax 3D-upgraded filtration Planmeca 4 5 Maxillary anterior Al-Okshi (2013) Veravieweposcs 3D J Morita 4 4 Maxillary anterior Al-Okshi (2013) a H W = height width. b Spherical field of view. c Extrapolated or averaged dose

212 4731 TABLE G.5 Effective doses for standard or default exposures for small FOV CBCT units (<10 cm height) mandibular views. Unit Name Manufacturer FOV Size H W a (cm) Region of Interest kvp mas Effective Dose (µsv) Reference 3D exam Kavo 4 16 Mandible Schilling (2013) 3D exam Kavo 5 10 Mandible b Jeong (2012) AZ3000CT Asahi 7 7 Mandible Jeong (2012) CB Mercuray Hitachi 10 Mandible b Jadu (2010); Ludlow (2008) DCT PRO VATECH 7 16 Mandible Qu (2012a) i-cat FLX Imaging Sciences 6 16 Mandible Ludlow (2013) i-cat NG Imaging Sciences 6 16 Mandible b Davies (2012); Morant (2013); Pauwels (2012); Roberts (2009); Theodorakou (2012) Implagrapy VATECH 5 8 Mandible Jeong (2012) Pan exam Plus 3D Kavo 6 4 Mandible Schilling (2013) Pan exam Plus 3D Kavo 6 8 Mandible Schilling (2013) Picasso Trio VATECH 7 12 Mandible Pauwels (2012) Promax 3D-upgraded filtration Planmeca 5 8 Mandible b Qu (2010) 212

213 Scanora 3D Soredex Mandible Pauwels (2012) 3D Accuitomo 170 J Morita 4 4 Mandibular posterior CS 9000 Carestream 4 5 Mandibular posterior Veravieweposcs 3D J Morita 4 4 Mandibular posterior Pauwels (2012) Pauwels (2012) Al-Okshi (2013) a H W = height width. b Extrapolated or averaged dose. 213

214 4735 TABLE G.6 Effective doses for standard or default exposures for small FOV CBCT Units (<10 cm height) mandibular views. Unit Name Manufacturer FOV Size H W a (cm) Region of Interest kvp mas Effective Dose (µsv) Reference 3D exam Kavo 4 16 Mandible Schilling (2013) 3D exam Kavo 5 10 Mandible b Jeong (2012) AZ3000CT Asahi 7 7 Mandible Jeong (2012) CB Mercuray Hitachi 10 Mandible b Jadu (2010); Ludlow, 2008) DCT PRO VATECH 7 16 Mandible Qu (2012a) i-cat FLX Imaging Sciences 6 16 Mandible Ludlow (2013) i-cat NG Imaging Sciences 6 16 Mandible b Davies (2012); Morant (2013); Pauwels (2012); Roberts (2009); Theodorakou (2012) Implagrapy VATECH 5 8 Mandible Jeong (2012) Pan exam Plus 3D Kavo 6 4 Mandible Schilling (2013) Pan exam Plus 3D Kavo 6 8 Mandible Schilling (2013) Picasso Trio VATECH 7 12 Mandible Pauwels (2012) Promax 3D-upgraded filtration Planmeca 5 8 Mandible b Qu (2010) 214

215 Scanora 3D Soredex Mandible Pauwels (2012) 3D Accuitomo 170 J Morita 4 4 Mandibular posterior Pauwels (2012) CS 9000 Carestream 4 5 Mandibular posterior Pauwels (2012) Veravieweposcs 3D J Morita 4 4 Mandibular posterior Al-Okshi (2013) a H W = height width. b Extrapolated or averaged dose. 215

216 TABLE G.7 Effective dose was statistically associated with FOV size (p = ) Tukey HSD demonstrated substantial differences between large and small FOVs. Level Least Sq Mean (µsv) Large A 240 Medium A B 149 Small B

217 4742 TABLE G.8 Salivary gland dose was not associated with FOV size (p = ). Level Least Sq Mean (µgy) Large A 3,336 Medium A 2,779 Small A 2,

218 TABLE G.9 Thyroid dose (µgy) was statistically associated with FOV size (p = ). Tukey HSD demonstrated substantial differences between large and small FOVs. Level Least Sq Mean (µgy) Large A 1,450 Medium A B 645 Small B

219 TABLE G.10 Brain dose (µgy) was statistically associated with FOV size (p = ). Tukey HSD demonstrated substantial differences between large and small FOVs. Level Least Sq Mean (µgy) Large A 2,159 Medium A B 1,101 Small B

220 TABLE G.11 Small FOV maxillary versus mandibular doses were not statistically different by effective dose (p = ), brain (p = ), or salivary glands (p = ). Substantial differences in thyroid dose are present (p = ). Level Least Sq Mean (µgy) Mandible 616 Maxilla

221 4754 Appendix H Dental X-Ray Evaluation by Qualified Expert H.1 Radiation Safety Radiation Safety should be evaluated based on integrated exposure measurements using a dosimeter, taken at various locations within and near the x-ray source. It may be necessary to increase the milliamperage-seconds to obtain a reading on your survey instrument. Inquire about workload with the staff, controlled or noncontrolled occupancy of areas near x-ray sources, and verify by reviewing representative patient logs. These should be readily available on digital systems. The qualified expert should document that radiation exposures to occupationally exposed persons and the general public are in compliance with the applicable regulations CBCT systems are often located where panoramic units were previously installed. However, the scattered radiation dose from CBCT is substantially higher than for panoramic units (about an order of magnitude), due to the significantly larger field of view exposed in CBCT systems. Calculate the exposure to persons in the vicinity of the x-ray source following the principles of NCRP Report No. 147 and information provided in this report. While exposures and workloads may remain consistent from year-to-year for intraoral x-ray units, increased utilization of CBCT systems in recent years make it essential for the qualified expert to evaluate personnel exposure during each annual survey. At the very least, the qualified expert should recalculate estimated weekly exposures using initial area survey measurements and recent workload data. Results should be compared with requirements from the local jurisdiction. Pay particular attention to personnel who may be working within line of sight of a CBCT unit or in an adjacent room, and make appropriate recommendations to assure ALARA. 221

222 H.2 Evaluation of the Image Receptor and Dose If the facility is using dental film, determine whether they are using D-speed film, E-speed film, F-speed film, or what is referred to as E-F-speed film. This may require some detective work, if the film is purchased by mail in bulk. While many facilities have converted to digital image receptors, recent data shows that among those still using film 78 % continue to use D speed film (Farris and Spelic, 2015). The image quality for E-, F-, and E-F-speed films is similar to that obtained with D-speed film (Bernstein, 2003; FDA, 2014; Ludlow, 2001; Syriopoulos, 2001) at approximately one-half of the radiation dose (Table H.1). More information on the different speed films and image quality can be found at Table H.1 provides other helpful information.. The average exposure for D-speed film is ~2.3 mgy. This is much higher than necessary. D-speed film should be on the order of 1.50 to 1.95 mgy (Table 6.1). In other words, there is no justifiable reason for dental doses to routinely exceed 1.95 mgy for D-speed film. Facilities that are using D speed film should be advised of the lower doses possible with the use of E or F speed films. They should also be advised of the potential for low doses with digital-based equipment as shown in the table H.3 Film Processing Conditions and Quality Processing conditions and quality have been found to vary considerably in the dental imaging community. Verify that proper time-temperature developing is being used. Film processing tips are included in Film processing is usually the weakest link in the imaging chain, with under-processing resulting in low contrast radiographs and increased patient doses. The histograms from the recent NEXT survey (Farris and Spelic, 2015) clearly demonstrate the broad range of patient doses and suboptimal film processing (approximately one-third of the facilities produce films with inferior contrast). To assist with testing processing conditions, consider an inexpensive step wedge or dental radiographic quality control device for

223 4811 TABLE H.1 Dental bitewing x-ray exposures (mr) for 2001, 2005, a Dental Bitewing for 2009 (n = 7,205) Speed Total % of Total Average SD Highest D 3, % ,150 E 1, % ,320 F % Digital 1, % Dental Bitewing for 2005 (n = 6,325) Type Total % of Total Average SD Highest D 3, % E 1, % F % Digital 1, % Dental Bitewing for 2001 (n = 8,600) Type Total % of Total Average SD Highest D 5, % ,308 E 1, % F % Digital 1, % a Courtesy New York State Department of Health

224 dental film processing quality. The dental radiographic quality control device is also helpful in assuring appropriate initial film exposure technique selection and processing conditions (Valachovic, 1981) H.4. Evaluation of the X-Ray Generator and Output The x-ray generator can be evaluation using standard techniques. Be sure that the radiation detector is properly positioned, and sized appropriately to include the complete x-ray beam. Modern units typically operate at only a single kilovoltage, 60 to 70 kvp, and a single milliamperage, 6 to 10 ma. Be sure to account for any effect of very short radiographic exposure times, i.e., overshoot of output for the first few milliseconds H.5 Evaluation of the Beam Collimation For intraoral radiographic units, consider recommending rectangular collimation, which has been shown to reduce effective dose four to five times by providing an x-ray beam that more closely approximates the rectangular image receptor (White and Pharoah, 2014). The qualified expert s experience with the benefits (image quality and radiation safety) derived from collimating the x-ray beam to the image receptor in body radiography and fluoroscopy (for example), will be directly applicable here Evaluating collimation for panoramic or CBCT systems requires some pre-planning, and may be accomplished using GAF Chromic Film and the equipment manufacturer s specifications for geometry. Figure H.1 shows how this may be accomplished H.6 Occupational Radiation Exposure Assessment While many dental offices are not required to use personal dosimetry, increased utilization of digital and CBCT imaging may warrant a renewed assessment of occupational exposure with personnel dosimetry. The qualified expert should advise the facility management whether occupational dosimetry is appropriate or is required by state or local regulations. 224

225 Fig. H.1. The photo on the left shows the self-developing x-ray film taped to the surface of the x-ray tube cover. The images at the right show two strips, following exposure (photos courtesy R. Pizzutiello)

226 4861 Appendix I Radiation Risk Assessment I.1 Introduction The assignment of risk of biological damage from radiation has long been an arena of considerable controversy. Damage from moderate to high doses are well documented and the risk well quantified. However, risks from small and very small doses are inferred from data for moderate to high doses based on one of several risk models. While there is growing new evidence, and strengthening of existing evidence, for damage from very low doses of radiation, there is considerable controversy over the methodology and conclusions in many of these studies, and the application of these population risks to individuals HPS, 2016; NCRP, 2010b; UNSCEAR, 2012). This is especially true in oral and maxillofacial imaging, where radiation doses (except for high resolution moderate-to-large field-of-view cone-beam CT imaging) are considerably smaller than in other fields of medical imaging. Nonetheless, dentistry as a profession has a responsibility for the radiation safety of the population-at-large as well as for the individual seeking care In the time since NCRP-145, Radiation Safety in Dentistry, there have been significant advances in the understanding of radiogenic DNA damage and repair, based on considerable laboratory research in genetics and molecular biology. Solidification of long-term studies of Japanese atomic bomb survivors, have increased confidence in risk estimates at low radiation doses. The understanding of genetic instability has given us a better understanding of the long latent periods associated with radiation carcinogenesis and heritable defects. Substantial publications elucidating the uncertainties in risk estimation have recently been published (NA/NRC, 2006; UNSCEAR, 2015b). Recent retrospective studies on large populations of head-irradiated children in the UNITED KINGDOM and in Australia, while eliciting some controversy over their epidemiologic methodology, have supported the existing risk modeling for radiogenic brain, thyroid, salivary gland and leukemia neoplasms (Brenner and Hall, 2007; 226

227 Mathews et al., 2013). A recent publication provides a clear and comprehensive review of cancer risks from diagnostic imaging (Linet et al., 2012) There must always be a balance between the benefit to the patient and the risk of damage to the patient when diagnostic x-radiation is used for imaging. There are many steps, recommended in this report, to maintain, or improve, the diagnostic quality of the images while minimizing the radiation dose to the patient a patient care application of the ALARA principle. The goal is always to maximize diagnostic efficacy while minimizing radiation dose I.2 Definitions I.2.1 Stochastic Effects These low-dose effects consist almost entirely of cancer and mutation. They are generally rare events, occurring only after a latent period of years to decades for cancer and generations for genetic effects. Thus, they present practical problems in the design of studies for their investigation. In the cohort of 87,000 Japanese atomic-bomb survivors, there were 9335 deaths from solid cancers between 1950 and 1997 attributable to radiation exposure (Preston et al., 2003). Recent analyses have confirmed and reinforced the risk estimates from the atomic-bomb survivor studies (Douple et al., 2011; Preston et al., 2007) Risks from low doses have been estimated by extrapolation from high dose data (ICRP, 1991; NA/NRC, 1990; 2006; NCRP, 1993b; UNSCEAR, 2000; 2015a). There has been considerable disagreement in the literature concerning the model used for such extrapolation to dose levels used in diagnostic imaging (AAPM, 2012). For radiation protection purposes, NCRP and most regulatory agencies worldwide use the most conservative, patient- and population-oriented modeling, and recommend use of the linear nonthreshold dose-response model for estimating the nominal risk of low doses (Douple et al., 2011; NA/NRC, 2006; NCRP, 1993b, 2009; Puskin, 2009; UNSCEAR, 2015a)

228 4921 I.2.2 Deterministic Effects (Tissue Reactions) Deterministic effects (also referred to as tissue reactions) result from structural or functional damage to tissue caused by irradiation. The type and amount of tissue damage increases with dose once a threshold is passed. When sufficient numbers of functional parenchymal cells in a given organ or tissue are killed, then the function of that organ or tissue may be impaired or destroyed. If that function is vital, then the injury may be life threatening to the organism. Classic examples of tissue reactions are the acute radiation syndromes (Rubin and Casarett, 1968), non-melanotic skin carcinogenesis and cataractogenesis. The dose thresholds for tissue reactions are sufficiently large that it is highly unlikely that a dental worker or a patient would suffer a tissue reaction, provided that common radiation safety precautions are followed I.2.3 Dose Language In this document, and throughout radiation biology and radiation health physics literature, the terms high, moderate, low and very low radiation doses or exposures are used. In this document, the terms are defined in effective dose units as follows (UNSCEAR, 2015a): average annual background radiation dose in the United States = 6.2 msv; high = greater than ~1 Sv; moderate = ~100 msv to ~1 Sv; low = ~10 to ~100 msv (dose to an individual from multiple whole-body CT scans and from multiple large field-of-view, high resolution CBCT scans); and very low = less than ~10 msv [dose to an individual from conventional radiology (i.e., without CT or fluoroscopy)]. 228

229 4947 I.3 Studies of Irradiated Human Populations I.3.1 Introduction The nature of the risk of carcinogenesis at low radiation doses has long been the subject of controversy. Major publications during recent years have focused on uncertainties in risk estimation at low doses (NCRP, 2012; UNSCEAR, 2015b). Several models have been developed to explain low dose risk, and these are shown in the graph below. The committee finds the linear nonthreshold (LNT) model to be a computationally convenient starting point. Actual risk estimates improve upon this simplified model by using a dose and dose-rate effectiveness factor (DDREF), which is a multiplicative adjustment that results in downward estimation of risk and is roughly equivalent to using the line labeled Linear Nonthreshold (low dose rate). The latter is the zero-dose tangent of the linearquadratic model. While it would be possible to use the linear-quadratic model directly, the DDREF adjustment to the linear model is used to conform with historical precedent dictated in part by simplicity of calculations. In the low-dose range of interest, there is essentially no difference between the two (adapted from Brenner and Elliston, 2004). A meta-analysis of data from cohorts with prolonged occupational exposure has indicated that risks per unit dose are consistent with those derived from the Life Span Study (LSS) cohort of the atomic bombing survivors (Jacob et al., 2009; UNSCEAR, 2015b). Recent evidence from continued analysis of cancer in Japanese survivors of the atomic bombings, radiation workers in the UNITED KINGDOM, Canada and the United States, and children exposed to diagnostic head CT exposures in Australia have provided substantial direct evidence that solid tumorigenesis follows the linear model and that leukemogenesis follows the linear-quadratic model. Most of the information on radiation risks therefore still comes from studies of populations with medium to high doses, with the notable exceptions of childhood cancer risk following in utero exposures and thyroid cancer risk following childhood exposures, for which significant increases have been shown consistently in the low- to medium-dose range (NA/NRC, 2006). 229

230 Fig. I.1. Models of low dose radiogenic cancer risk (NA/NRC, 2006)

231 Brenner et al. (2007), estimate that from 1.5 to 2 % of all cancers in the United States may be attributable to the radiation from CT studies. An annual growth rate of >10 % y 1 for CT procedures in the United States (NCRP, 2009) appears to be mirrored in the growth rate of CBCT since its introduction (Farris and Spelic, 2015) I.3.2 Atomic Bomb Survivor Lifetime Studies Survivors of the atomic bombings of Hiroshima and Nagasaki and their offspring comprise the single largest cohort exposed to ionizing radiation that is currently being followed, and are the major source of lifetime studies of radiation-induced cancers, other diseases, and life shortening. A major reevaluation of the dosimetry at Hiroshima and Nagasaki has recently been completed that lends more certainty to dose estimates and provides increased confidence in the relationship between radiation exposure and the health effects observed in this population Solid tumors that are well described by the linear model include female breast and thyroid, while leukemias appear to fit the linear-quadratic model best. This is shown in the graph below. Additional new information is also available from radiation worker studies, medical radiation exposures, and populations with environmental exposures. Although the cancer risk estimates have not changed greatly since the 1990 BEIR V report (NA/NRC, 1990), confidence in the estimates has risen because of the increase in epidemiologic and biological data available to the committee (Douple et al., 2011; NA/NRC, 2006) I.3.3 Children Irradiated for Tinea Capitis and Enlarged Thymus Studies on the risk of thyroid cancer following irradiation of the head for tinea capitis has been extensively followed, from post-ww2 through These studies have shown a clear risk when radiation occurred in childhood especially before 10 y of age. There was a fourfold increase in the incidence of thyroid cancer and a twofold increased incidence in benign thyroid tumors (Ron et al., 1989). Additionally, there was a 4.5-fold increase in the incidence of

232 Fig. I.2. Excess relative risks of solid cancer for Japanese atomic bomb survivors. Plotted points are estimated excess relative risks of solid cancer incidence (averaged over sex and standardized to represent individuals exposed at age 30 y who have attained age 60 y) for atomic bomb survivors, with doses in each of 10 dose intervals, plotted above the midpoints of the dose intervals. Vertical lines represent approximate 95 % confidence intervals. Solid and dotted lines are estimated linear and linear-quadratic models for excess relative risk, estimated from all subjects with doses in the range 0 to 1.5 Sv. A linear-quadratic model will always fit the data better than a linear model, since the linear model is a restricted special case with the quadratic coefficient equal to zero. For solid cancer incidence however, there is no statistically significant improvement in fit due to the quadratic term. It should also be noted that in the lowdose range of interest, the difference between the estimated linear and linear-quadratic models is small relative to the 95 % confidence intervals. The insert shows the fit of a linear-quadratic model for leukemia to illustrate the greater degree of curvature observed for that cancer (NA/NRC, 2006) (adopted from NA/NRC, 2006, Figure ES-1)

233 malignant salivary gland tumors and a 2.6-fold increase in benign salivary gland tumors in the same population (Modan et al., 1998) Children in Rochester, NY who received X-ray treatment for enlarged thymus glands between 1926 and 1957 prior to six months of age showed statistically significant increases of both benign and malignant thyroid tumors (Shore et al., 1985), as well as tumors of bone, nervous system, salivary glands, skin and female breast (Hildreth et al., 1985). The most recent study (Shore et al., 1993) again showed increased risk of thyroid cancer, even at low doses These data all fit well with a LNT model for thyroid carcinogenesis in children I.3.4 Females Receiving Fluoroscopy for Tuberculosis Treatment Follow-up Significant increases in breast cancer was found in a cohort study of 64,172 tuberculosis patients of whom 25,007 received highly fractionated radiation from repeated fluoroscopy for lung collapse treatment of tuberculosis. There was a significant increase in risk of breast cancer in a dose dependent manner, commensurate with the LNT model (Boice et al., 1991). The excess cancer risk did not occur until 15 y after exposure, and held for over 50 y (Boice et al., 1991a; Davis et al., 1989; Howe and McLaughlin, 1996; Miller et al., 1989; NA/NRC, 2006) I.3.5 United Kingdom National Registry of Radiation Workers This study has provided the most recent, direct estimates of long-term, low-dose, low-let radiation effects on occupationally exposed populations, and has provided estimates of leukemia and all solid cancer risks. Risks, comparable to those in the atomic bomb survivors, range from slightly below to twice above those estimated using the current linear, nonthreshold model. The ERR/Gy calculated from the Nuclear Industry Workers study was comparable with risk estimates for atomic bomb survivors for both solid tumors and leukemias (Muirhead et al., 2009)

234 Fig. I.3. Incidence rate ratio (IRR) for all types of cancer in exposed versus unexposed individuals, by number of CT scans (Matthews et al., 2013)