The use of ionizing radiation in medical and

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1 SHORT COMMUNICATION Radiation protection guidelines for the practicing orthodontist Muralidhar Mupparapu Newark, NJ This article summarizes the most recent (December 2003) dental x-ray guidelines from the National Council on Radiation Protection and Measurements report #145. The guidelines are intended for all dental health-care providers. They address radiation dose limits for occupational and nonoccupational exposure and radiation protection for operators, patients, and the public. Equipment design can play an important role in radiation protection, and recommendations from the guidelines are discussed. (Am J Orthod Dentofacial Orthop 2005;128:168-72) The use of ionizing radiation in medical and dental health care is well regulated in the United States. The federal government has established performance standards for the manufacture and installation of x-ray equipment designed for clinical use. 1,2 In addition, some states have implemented regulations that govern users, including dentists. These regulations deal with the design of facilities, especially radiation shielding, and the use and maintenance of equipment. The National Council on Radiation Protection and Measurements (NCRP) is a nonprofit organization chartered by Congress in 1964 to collect, analyze, develop, and disseminate information and recommendations in the public interest about (1) protection against radiation and (2) radiation measurements, quantities, and units related to radiation protection. The NCRP is working to develop basic guidelines about radiation quantities, units, and measurements and their application to the field of radiation protection. BIOLOGICAL EFFECTS OF RADIATION Biological effects of radiation fall into 2 categories: deterministic and stochastic. Deterministic effects occur in anyone who receives a dose of radiation that exceeds a certain threshold. The severity of the effect is proportional to the dose. Examples include acute radiation sickness, cataracts, and epilation. Stochastic effects, such as cancer, are all-or-none effects. Either a Associate professor and director, Division of Oral and Maxillofacial Radiology, Department of Diagnostic Sciences, University of Medicine and Dentistry of New Jersey Dental School. Reprint requests to: Dr M. Mupparapu, Diagnostic Sciences, D-860, New Jersey Dental School, 110 Bergen St, Newark, NJ ; , m.mupparapu@umdnj.edu. Submitted, November 2004; revised and accepted, April /$30.00 Copyright 2005 by the American Association of Orthodontists. doi: /j.ajodo radiation-induced cancer occurs or it does not. There is no threshold. The NCRP has established recommended dose limits for occupational and public exposure (Table I). Annually, the average person in the United States receives about 100 mrem (1mSv) of natural background radiation excluding the radon measurement. The radiation protection recommendations pertain to man-made sources other than medical and dental diagnostic x- radiation. For continuous or repeated exposures, the annual effective dose limit is 100 mrem or 1 msv. Published data 3 indicate that average dental occupational exposures are generally a small fraction of the limit and are far less than that of most other health-care workers (Table II). NCRP report #145 supersedes the report for dentistry, #35, published in The NCRP uses shall and shall not as well as should and should not in its report. Shall and shall not mean that adherence to the recommendation is considered necessary to meet accepted standards of protection. Should and should not are used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances. Although the guidelines cover broad areas for the general dental practitioner, orthodontists should be especially concerned with the recommendations for extraoral radiography, including panoramic, lateral, and posteroanterior cephalometric views. The general guidelines govern the use of leaded aprons and thyroid collars, rectangular collimation for intraoral radiographs, selection criteria, radiation protection programs in offices, radiation safety training for all staff, measures to minimize sight development for evaluation of films, and qualified experts to determine the shielding 168

2 American Journal of Orthodontics and Dentofacial Orthopedics Volume 128, Number 2 Mupparapu 169 Table I. NCRP recommended radiation dose limits for occupational and public exposure Dose limits Basis Stochastic Deterministic effects Embryo and fetus 1 msv (0.001Sv) 0.1 rem. *1 Sv 100 rem. Occupational 5 rem (50 msv)* annual effective dose 1 rem (10 msv) age (y) cumulative effective dose 15 rem (150 msv) for lens of eye 15 rem (150 msv) for skin, hands, and feet 0.05 rem (0.5 msv)/month once pregnancy is known Public 0.1 rem (1 msv) frequent exposure 0.5 rem (5 msv) for infrequent exposure 1.5 rem (15 msv) for lens of eye 5 rem (50 msv) for skin, hands, and feet Table II. Average dental exposure by mean whole-body dose (WBD) to health-care workers compared with other occupations (data from Kumazawa et al 3 and NCRP 1 ) Measurement Occupational subgroup Type of exposure Hospital Medical offices Dental Podiatry Chiropractic Veterinary Total WBD for all workers with potential occupational exposure (msv) WBD in workers who are exposed (msv) msv 0.1 rem. requirements for new equipment or when an older facility is remodeled. In addition, report #145 covers collimation guidelines for cephalometric and panoramic radiography. This will be discussed later in this article. The NCRP report includes some general guidelines for all clinicians: 1. No one shall be permitted to receive an occupational effective dose in excess of 5 rem (50 msv) in any year (Table I). 2. Facility design, x-ray equipment performance, and operating procedures should be established to maintain patient, occupational, and public exposures as low as reasonably achievable, with economic and social factors taken into account. 3. All radiographic examinations shall be performed only on direct prescription of the dental practitioner or physician after a clinical history and physical examination of the patient, and determination of a reasonable expectation of a health benefit to the patient. The report also lists radiation protection guidelines for patients: 1. For each new or referred patient, the dentist shall make a good-faith attempt to obtain recent, pertinent radiographs from the patient s previous dentist. Radiographic examinations shall be performed only when indicated by patient history, physical examination, or laboratory findings. 2. For symptomatic patients, the radiographic examination shall be limited to images that are required for the treatment planning of the current disease. 3. For asymptomatic patients, the radiographic examinations should be conducted based on published selection criteria Administrative use of radiation shall not be permitted. 5. Radiation exposure that is desirable per image is generally a function of the film/receptor speed and based on published diagnostic reference levels at skin entry; their applicability varies from state to state The x-ray equipment shall meet or exceed all applicable government requirements and regulations. Portable x-ray machines shall not be used when fixed installations are available. 7. The operating potential of the x-ray machines should be between 60 and 80 KVp. The operating potential should not be lower than 50 KVp or higher than 100 KVp. 8. All position-indicating devices shall be open-ended with provision for attenuation of scattered radiation arising from the collimator or filter. 9. Source-to-image receptor distance for intraoral radiography should not be less than 40 cm. 10. Rectangular collimation of the x-ray beam shall be routinely used for periapical and bitewing radiography (Fig 1).

3 170 Mupparapu American Journal of Orthodontics and Dentofacial Orthopedics August Image receptors of speeds slower than American National Standards Institute (ANSI) 11 speed E films shall not be used for intraoral radiography. Faster films should be evaluated and used if acceptable. 12. For extraoral dental radiographic projections, high-speed (400 or greater) rare-earth screen-film systems or digital imaging systems of equivalent or greater speed shall be used. 13. Dental radiographic films shall be developed according to the time-temperature method and the chemistry according to the manufacturer s instructions. Sight development shall not be used. 14. Use of leaded aprons for full mouth or panoramic examinations is a prudent but not essential practice. Gonadal doses from current full-month series or panoramic examinations do not exceed 5 Gy ( rad). 9 A significant portion of this gonadal dose results from scattered radiation in the patient s body. Leaded aprons do not significantly reduce these doses. 1 The guidelines state that leaded aprons on patients are not required if all other recommendations in the report are rigorously followed. 15. Thyroid collars shall be provided for children and should be provided for adults (Fig 2), when they will not interfere with the examination. The report includes guidelines to protect the operator: Fig 1. Rectangular collimator (arrow) attached to openended round x-ray position-indicating device (PID) Fig 2. Thyroid collar and lead apron for intraoral radiography. 1. New or remodeled offices should have shielding designed by a qualified expert to create adequate protective barriers. The barriers shall be constructed so that operators can maintain visual contact and communication with patients throughout the procedures. 2. The operator should be standing at a minimum distance of 2 meters from the tube head. If this minimum distance cannot be maintained, a barrier shall be provided. 3. Monitoring of individual occupational exposures for office staff and personnel is required for those reasonably expected to receive a significant dose. The NCRP recommends personal dosimeters for external exposure measurement for workers who are likely to receive an annual effective dose in excess of 1 msv and also for pregnant occupationally exposed personnel. Finally, the report outlines steps that should be taken to protect the public, including people in reception rooms, other treatment areas in the same office, and adjoining corridors in the building. New dental facilities shall be designed so that no member of the public will receive an effective dose in excess of 100 mrem or 0.1 rem (1 msv) annually. EQUIPMENT DESIGN For optimal use of radiation in dentistry, the Food and Drug Administration has developed performance standards for medical and dental x-ray machines. Compliance with these standards at installation is required for all machines manufactured in the United States after The NCRP recommends that the x-ray machines shall provide the range of exposures that are suitable for use with the fastest image receptors available. It is the responsibility of the clinician who owns the office to make sure that the tube head is free of drifts and oscillations. The operator is prohibited from holding the tube head during exposure. 10

4 American Journal of Orthodontics and Dentofacial Orthopedics Volume 128, Number 2 Mupparapu 171 Equipment design for intraoral radiography shall be capable of providing rectangular collimation. Collimating the x-ray beam to the precise size of the image receptor eliminates scatter radiation. Scatter radiation in general decreases the quality of the image. Rectangular collimation of the beam shall be used routinely for periapical radiography. Each dimension of the beam measured in the plane of the image receptor shall not exceed the dimension of the image receptor by more than 2% of the source-receptor distance. Similar collimation should be used when feasible for interproximal (bitewing) radiography. SPECIFIC GUIDELINES FOR THE ORTHODONTIST For all intraoral radiography, the NCRP recommends using ANSI 11 film speeds E and above when available. For extraoral radiography, blue fluorescing calcium tungstate screens that are considered slow are no longer recommended because they increase the patient s skin and absorbed x-ray dose. The specific NCRP recommendation is: The fastest imaging system consistent with the imaging task shall be used for all extraoral dental radiographic projections. High speed (400 or greater) rare-earth screenfilm systems or digital systems of equivalent or greater speed shall be used. For direct digital radiograpy, in which the filmbased image is replaced by a digital image consisting of a 2-dimensional array of pixels, the latent image is recorded directly on a suitable digital sensor. Receptors include photostimulable phosphors, charge-coupled devices, and complementary metal-oxide semiconductors, which are also known as active pixel sensors. The latent image is later digitally processed to produce an electronic image. The electronic image can be displayed on a computer monitor, converted to a hard copy, or transmitted electronically. Although the guidelines discuss the use of direct digital radiography at length, there are no specific recommendations to replace the existing fast film for intraoral radiography. The report agreed with the current published literature regarding the detection efficiency of digital receptors with that of conventional film when investigating occlusal and proximal caries, periodontal bone lesions, periapical bone lesions, and root canal systems Rotational panoramic machines use a narrow vertical beam, exposing only a small portion of the image receptor at any time. The NCRP s recommendation is: 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. In no case shall it be larger than the slit in the image-receptor carrier plus a tolerance of two percent of the source-to-image receptor distance. Clinicians who routinely perform cephalometric radiography should note the following. Generally, the area of clinical interest in cephalometric radiography is significantly smaller than the image receptor. The central axis of the beam is usually aligned through the external auditory canals, positioned by the ear rods of the cephalostat. Imaging of the structures superior to the superior orbital rim, posterior to the occipital condyles, and inferior to the hyoid bone is clinically unnecessary. This prevents unnecessary exposure to the patient s hard and soft tissues. It is also a standard recommendation from the NCRP that the soft tissue facial profile should be imaged along with osseous structures of the face. This is accomplished by reducing exposure to anterior soft tissues. Clinicians should switch from the slower, blue fluorescent screens to the faster green fluorescent screens. Kodak T mat G or Kodak Ektavision 15 (Eastman Kodak Company, Rochester, NY) screens with their speed-matched film combinations are examples of fast screens. Filters for imaging the soft tissues of the facial profile and the facial skeleton shall be placed at the x-ray source rather than at the image receptor. This equipment modification might not be easy to achieve without purchasing new cephalometric or panoramiccephalometric combination machines (Fig 3). The new digital cephalometric machines come with this kind of built-in soft tissue filtering. This might be an added incentive for the practitioner to convert to digital receptors when replacing older equipment. The dose reduction might be substantial, because digital systems are much thriftier than existing screen-film systems, and the built-in soft tissue filters will eliminate the external cassette-side filtration. According to the NCRP report, Practitioners need to remember that all structures recorded on the image need to be interpreted for evidence of disease or injury as well as for cephalometric analysis. CONCLUSIONS NCRP report #145 is relatively new, and many in the dental profession have not yet taken a serious look at it. This important report defines standards of care in terms of radiation protection for the operator, the patient, and the public. It is certain to make an impact on the radiographic practices in most oral health-care settings. 16 It is the responsibility of all dental healthcare providers to reexamine their practices, equipment, protective devices, and receptor selection. Clinicians should consider converting to digital radiographic modalities for improved compliance, radiation dose reduction, and ease of storage, retrieval, and transfer of information.

5 172 Mupparapu American Journal of Orthodontics and Dentofacial Orthopedics August 2005 Fig 3. Newer-generation digital radiography machine has built-in soft tissue filter. (Planmeca Promax panoramic-cephalometric combination machine). REFERENCES 1. National Council on Radiation Protection and Measurements. Radiation protection in dentistry (report no. 145). Bethesda, Md: NCRP; Food and Drug Administration. Performance standards for ionizing radiation emitting products, 21 CFR Sect (1995). 3. Kumazawa S, Nelson DR, Richardson ACB. Occupational exposure to ionizing radiation in the United States: a comprehensive review for the year 1980 and a summary of trends for the years EPA 520/1-84/005 (National Technical Information Service, Springfield, Va). 4. National Council on Radiation Protection and Measurements (NCRP). Dental x-ray protection (report no. 35). Bethesda, Md: NCRP; Joseph LP. The selection of patients for x-ray examinations: dental radiographic examinations. HHS Publication No. FDA Rockville, Md: The Dental Radiographic Patient Selection Criteria Panel, DHHS, Center for Devices and Radiological Health; Matteson SR, Joseph LP, Bottomley W, Finger HW, Frommer HH, Koch RW, et al. The report of the panel to develop radiographic selection criteria for dental patients. Gen Dent 1991;39: ADA Council on Scientific Affairs. An update on radiographic practices: information and recommendations. J Am Dent Assoc 2001;132: Conference of Radiation Control Program Directors, Inc. Patient exposure and dose guide. CRCPD publication E Frankfort, Ky: Conference of Radiation Control Program Directors Inc; White SC assessment of radiation risk from dental radiography. Dentomaxillifac Radiol 1992;21: International Electrotechnical Commission. Medical electrical equipment. Part I: general requirements for safety. 3. Collateral standard: general requirements for radiation protection in diagnostic x-ray equipment. SS-EN Geneva, Switzerland: International Electrotechnical Commission; American National Standards Institute. Photography-intraoral dental radiographic film specifications: ANSI/ISO New York: Amercican National Standards Institute; Kullendorf FB, Nilsson M, Rohlin M. Diagnsotic accuracy of direct digital dental radiography for the detection of periapical bone lesions: overall comparison between conventional and direct digital radiography. Oral Surg Oral Med Oral Pathol Radiol Endod 1996;82: Hintze H, Wenzel A, Jones C. In vitro comparison of D and E speed film radiography, RVG and Visualix digital radiography for the detection of enamel approximal and dentinal occlusal caries lesions. Caries Res 1994;28: Sanderink GC, Huiskens R, van der Stelt PF, Welander US, Stheeman SE. Image quality of direct digital intraoral x-ray sensors in assessing root canal length. The RadioVisioGraphy, Visualix/ VIXA, Sens-A-Ray and Flash Dent systems compared with Ektaspeed films. Oral Surg Oral Med Oral Pathol 1994;78: Kodak T-MAT G dental film and Kodak Ektavision G dental film. Available at: Accessed November 20, Accessed April 27, Miles DA, Langlais RP. NCRP report no New dental x-ray guidelines: their potential impact on your dental practice. Dent Today 2004;9: COMMENTARY The NCRP guidelines state that all radiographic examinations shall be performed only on direct prescription of the dental practitioner or physician after conduct of a clinical history and physical examination of the patient, and determination of a reasonable expectation of a health benefit to the patient. The guidelines also direct clinicians to make a good-faith attempt to obtain recent, pertinent radiographs from the patient s previous dentist. Radiographic examinations shall be performed only when indicated by patient history, physical examination or by laboratory findings. It has become common practice in orthodontic clinics to quick start potential patients on the first visit to the office. Some practice consultants advise giving the prospective patient an office tour that includes a stop at the x-ray machine to take panormic and cephalometric films, before introducing the patient to the orthodontist. This is done under the assumption that many patients will actually begin treatment that day, including spacers. Of course, not all prospective patients are ready to start treatment immediately or to commit to being treated at that particular office, so this practice results in unnecessary exposure for some and is a violation of the guidelines. Also, more effort should be made to obtain previously taken films to avoid duplication of exposure, even though it seems faster and more cost-efficient to take new films. This is a good example of the push/pull of orthodontic marketing and the resulting impact on patient care. Jan Bell Seattle, Wash Am J Orthod Dentofacial Orthop 2005;128: /$30.00 Copyright 2005 by the American Association of Orthodontists. doi: /j.ajodo