The x-rays produced penetrate the body which absorbs, refracts, or reflects the x-ray beam energy depending on the tissue. Bone

Authors Sari Cohen, Poh Yan Lim, Merng Koon Wong, Siew Hong Lau, Donna Russell-Larson 1.6.2 Image intensifier Poh Yan Lim, Merng Koon Wong The discovery of x-rays had a profound impact on the diagnosis and management of fractures. The subsequent development, introduction, and improvement of image intensifier technology has had an equally profound impact on trauma surgery as it allows immediate verification of fracture reduction and accurate positioning of orthopaedic implants on bone. However, as with any medical equipment, the benefits, risks, and limitations must be thoroughly weighed and balanced. Ionizing radiation Ionizing radiation is electromagnetic or particulate radiation capable of producing ions, directly or indirectly, in its passage through tissue. It alters atoms by removing one or more electrons, leaving positively charged particles known as free radicals. These free radicals may cause changes in DNA causing it to mutate and this can set off the development of malignancies. The amount of damage done by ionizing radiation depends on the dose received. Alpha and beta particles, gamma rays, and x-rays are all forms of ionizing radiation. X-rays and gamma rays are forms of short wavelength electromagnetic radiation. Diagnostic imaging There are three primary components in an x-ray imaging system, ie, an x-ray source, the object to be x-rayed, and a system for detecting and displaying the resultant image. The x-ray source produces x-rays using high-voltage electricity in a vacuum. The operator is able to focus the beam in a process called collimation. The smaller the area focused, the sharper the x-ray image and the smaller the dose. Collimation is exactly the same process as the setting of the aperture on a conventional camera (Fig 1.6-5). The operator is also able to select predetermined settings of an x-ray exposure dose and to initiate the exposure. The x-rays produced penetrate the body which absorbs, refracts, or reflects the x-ray beam energy depending on the tissue. Bone Open beam Collimated beam More tissue irradiated Less tissue irradiated More image degradation Less image irradiated a b Fig 1.6-5a b Collimation. 85 PORP_Book.indb 85 5/7/10 11:15:28 AM

Introduction 1.6 Equipment will reflect and absorb most x-rays while soft tissue will allow penetration. It is this differential of x-ray penetration which results in being able to visualize human bone and joint anatomy using x-rays. When x-rays reach the target-imaging plate and are absorbed, they cause certain substances on the imaging plate to fluoresce; thus emitting photons of lower energy. This is how x-rays can produce an image on a photosensitive film which can then be made visible by developing it. Alternatively, an x-ray sensitive cartridge is used which is developed to produce an electronic version of the image which is downloaded onto a computer network. An image intensifier captures this fluorescence in real time, transmitting it to a screen. X-ray dose is measured using the Gray scale (Gy), an international unit of absorbed dose. The image intensifier has three main parts the x-ray tube, the image intensifier collector, and the display screen (Fig 1.6-6). Note that x-rays come from the tube and are fired toward the collector. For good-quality images the beam of the x-ray should travel perpendicular to the limb/bone with the image intensifier receptor as close to the patient as possible. The source-to-patient distance must be at least 38 cm for image-intensified fluoroscopic units. Hazards of radiation exposure Everyone is subjected to background radiation and most is derived from cosmic rays. Some comes from the earth itself and small amounts from medical and other artificial sources. These background levels are always present and pose little hazard. 3. Display screen 2. Image intensifier collector 1. X-ray tube Fig 1.6-6 The three parts of an image intensifi er and x-ray tube. 86 Techniques and Principles for the Operating Room Porteous, Bäuerle PORP_Book.indb 86 5/7/10 11:15:31 AM

Authors Sari Cohen, Poh Yan Lim, Merng Koon Wong, Siew Hong Lau, Donna Russell-Larson Radiation sources are found in a wide range of occupational settings. If radiation is not properly controlled, it can be potentially hazardous to the workers health and can lead to development of cancer in sensitive organs, particularly in the thyroid and in bone marrow. The developing fetus is particularly at risk and exposure should be minimized in pregnancy. Exposure to x-rays is cumulative; thus, long periods between doses do not lessen the risks. 1.6.2.1 Radiation safety Although modern x-rays have minimal radiation effects on the patient, frequent, prolonged, and repetitive use of intraoperative image intensification have greatly increased the risk of significant radiation exposure to the surgical teams. It is the responsibility of every surgeon to be familiar with the image intensifier and to know how to minimize radiation exposure to himself/herself, the patient, and other members of the surgical team. Image intensifier machines which are able to store and then show the images taken have the effect of greatly reducing the radiation dose to which the patient and the surgical teams are exposed. Individual dose and risk limits The ICRP recommends that exposure of individuals should be subjected to dose limits, aimed at ensuring that no individual is exposed to unacceptable risks. Certain harmful effects of radiation, such as cataract formation, are dependent on dose. Patients and staff exposed to radiation below a certain dose (threshold dose) are not at risk of developing this complication. These effects are called deterministic. Other harmful effects of radiation do not have a threshold dose. The adverse effects which can include cancers are related to the absorbed dose but any exposure can potentially be harmful. These effects are called stochastic. The aim is to prevent any deterministic effects and minimizing the chance of stochastic effects (Tab 1.6-1). The most important principle of radiation protection is to keep all doses As Low As Reasonably Achievable while still allowing the beneficial use of ionizing radiation. The recommendations of the ICRP can be applied at several levels to control the hazards from radiation. The system of radiation protection recommended by the International Commission on Radiological Protection (ICRP) in Publication 60 is based on three major principles: Justification of practice A practice which involves exposures or potential exposures should only be adopted if it is likely to produce sufficient benefit to the individual or society to outweigh the detriment or harm to health. Optimization of protection ALARA principle Individual doses, the number of people exposed, and the likelihood and magnitude of potential exposures should be kept As Low As Reasonably Achievable (ALARA), economic and social factors being taken into consideration. Application Effective dose Annual equivalent dose in: lens of the eye skin hands and feet Dose limit occupational 20 msv per year, averaged over defined periods of 5 years 150 msv 500 msv 500 msv Tab 1.6-1 Recommended dose limits. Correct patient 1 msv in a year 15 msv 50 msv 87 PORP_Book.indb 87 5/7/10 11:15:34 AM

Introduction 1.6 Equipment Regulatory requirements The ICRP and many national regulatory agencies worldwide adopt a conservative stance with regard to radiation protection in radiology and medicine. The reason is that evidence surrounding low-dose radiation and its resulting risks is inconclusive. Foundation for a safety program Absorbed dose is related to duration, distance, and shielding. The three major techniques to maintain the ALARA principles are reducing duration of exposure, increasing the distance to the source of exposure, and shielding. The formulation and implementation of regulations and legislation varies from country to country. Regulations provide a link between the ICRP recommendations and their implementation in the workplace. The regulations define a satisfactory standard of protection and apply to all justified practices. Management requirements Management has the important role of implementing system safeguards for quality control and safety. It should also take potential exposures into account and institute risk analysis to identify possible causes of incidents and limit the probability and effect of such incidents. Regular quality control tests should be done to detect deterioration in equipment performance to minimize undue patient and staff radiation exposure. One of the main responsibilities of this management is to encourage a good attitude to safety and recognition that safety is a personal responsibility. In addition, the management should optimize protection by clearly defining responsibilities and providing clear and simple operating instructions. Monitoring Absorbed dose by staff members needs to be monitored by means of thermoluminescent dosimeters (TLDs) and personal pocket dosimeters. TLDs are able to record total exposure, while pocket dosimeters are used to immediately determine radiation exposure. They are to be worn at the waist level and are the most accurate form of monitoring workers exposure to radiation. Duration Minimizing the duration of exposure directly reduces the radiation dose: Keep beam-on time to a minimum Inform the radiographer where the C-arm is positioned Perform a trial screening in the planned projections after positioning of patient Take only the minimum number of images required Rely on stored images without the need for reexposure Minimize use of magnification (source close to limb) Collimate the image whenever possible Use single-pulsed mode image intensification and pulsedscreening mode, instead of continuous image intensification. Studies suggest that screening time is controlled predominantly by the surgeon Controlling the dose received by the patient will helps in turn control the dose for the staff Distance The further you are from an x-ray source, the less radiation you will receive. The inverse square law states that the dose of radiation received is inversely proportional to the square of the distance from the x-ray source. Therefore, increasing the distance between you and the source of radiation a little bit will significantly reduce the dose of radiation received. Doubling the distance reduces the radiation to a quarter. Shielding Exposure to radiation is reduced if dense-absorbing material such as lead and concrete are used to surround x-ray units. The doors and walls of operating rooms designated for image intensification 88 Techniques and Principles for the Operating Room Porteous, Bäuerle PORP_Book.indb 88 5/7/10 11:15:36 AM

Authors Sari Cohen, Poh Yan Lim, Merng Koon Wong, Siew Hong Lau, Donna Russell-Larson should be shielded with lead and made of reinforced concrete, respectively (Fig 1.6-7). Protective equipment for staff (Fig 1.6-8) and patients must be provided and used. The following are recommended: Gowns/aprons/skirt/vest with 0.5 mm lead equivalent for surgical teams Neck shields to protect the thyroid Lead glasses decrease exposures of the eyes, 0.15 mm lead equivalent goggles provide 70% attenuation beam energies Gonad shielding of at least 0.25 mm lead equivalence must be used on patients of reproductive age, if the gonads are in the primary beam and the shielding does not interfere with the diagnostic procedure Lead screens provide additional protection of OR personnel who do not wear lead protection. Viewing glass materials must have the same lead equivalence as the shield Scattered radiation under the table must be attenuated by at least 0.25 mm lead equivalence shielding Walls, ceiling, doors, and floor areas of rooms housing diagnostic units must be provided with sufficient protective shielding (lead or lead equivalent materials) Fig 1.6-7 Leaded door. Fig 1.6-8 Proper protective equipment and lead screen for OR staff. 89 PORP_Book.indb 89 5/7/10 11:15:38 AM

Introduction 1.6 Equipment Note that the reduction in radiation dose provided by a lead apron depends on its physical condition, how it is worn, its lead equivalence, and the strength of the x-ray beam. Lead aprons cover about 75 80% of a person s active bone marrow. Crumpling of the lead apron will break the integrity of the lead-fiber shielding, reducing its effectiveness. Therefore, lead aprons should be properly hung up after use and not folded in any manner (Fig 1.6-9). The maximum scatter comes from the side of the patient that is closest to the x-ray tube (Fig 1.6-10). The side of the patient closest to the image intensifier gives off less scatter because the direct beam and scattered radiation are reduced as they pass through the patient due to absorption. Scatter Not all x-rays pass through the object on which they are focused. Some are also reflected and refracted as they penetrate through the object resulting in scatter. Members of the surgical team standing close to the patient are at particular risk of exposure from scatter. It is therefore important to understand how this can be minimized. Image intensifier 1.2 3 12 6 X-ray tube a Fig 1.6-9a b a Proper care of aprons. b Improper care of aprons. b 0 m 0.5 m 1 m Fig 1.6-10 Scatter dose diminishes with distance. 90 Techniques and Principles for the Operating Room Porteous, Bäuerle PORP_Book.indb 90 5/7/10 11:15:43 AM

Authors Sari Cohen, Poh Yan Lim, Merng Koon Wong, Siew Hong Lau, Donna Russell-Larson Therefore, during image intensification, whenever possible: The x-ray beam should be aimed in such a way that the scatter is going toward the floor and not into the surgical team. In practice this means placing the x-ray tube under the patient. The image intensifier receptor should be kept as close as possible to the patient (Fig 1.6-11). This not only reduces scatter but also improves image quality and reduces radiation dose. Since the amount of scatter produced increases with the size of the area irradiated, it is good practice to restrict the field size to the area receiving imaging. Staff exposure can be limited by keeping as far from the beam as physically possible when an image is being obtained. In the lateral projection, the source (ie, x-ray tube) is usually at the surgeon s side; the surgical team should stand further away from the source, and no one should stand directly behind the image intensifier receptor itself as x-rays are aimed directly at it. Surgeons and assistants who must face the operation site during the use of the image intensifier should avoid being positioned directly in the beam (Fig 1.6-12). X-ray tube Image intensifier msv/h at 0.5 mm msv/h at 1 m Patient distance = 1 m 100 kv 1 ma 3.2 msv/h) 0.8 msv/h) 3.2 msv/h) 0.6 msv/h X-ray tube Patient thickness = 18 cm 3.2 msv/h) 0.3 msv/h Fig 1.6-11 Image intensifi er positioned as close as possible to the patient. 0 m 0.5 m 1 m Fig 1.6-12 Note the effectiveness of distance relating to the received scattered radiation dose. 91 PORP_Book.indb 91 5/7/10 11:15:50 AM

Introduction 1.6 Equipment 1.6.2.2 Documentation Every hospital must have a radiation safety protocol as an integral part of the occupational health and safety program. Although regulations and practice varies in different parts of the world, the following principles should apply: Written policies and procedures address compliance with applicable standards, laws, and regulations Attendance at the radiation safety awareness program for hospital staff is mandatory All employees who are exposed to radiation are registered and are assigned personal thermoluminescent dosimeter (TLDs) to monitor their radiation exposure: The regulatory authority will issue a new TLD every 2 months and report the result TLDs have to be worn at the waist level, beneath a lead apron Handling of lead aprons: Lead aprons are tagged with an ID, and are inspected annually Reports are to be filed by the user department Proper metal racks constructed to hang the lead aprons must be used when aprons are not in use Posting and labeling: All operating rooms with x-ray/image intensifier machines shall be clearly and visibly labeled to caution individuals that such machines produce radiation when operated Radiation safety inspection checklist to aid in auditing/ inspecting radiation areas should be created Radiation safety and radioactive waste disposal manuals made available in the hospital intranet All x-ray machines come with a use log requiring the following information each time the machine is used: Date of use Name of the operator Description of use Beam voltage, beam current Time beam turned on and off Comments concerning operation abnormalities, repairs, and so on Conclusion Increased use of x-ray and image intensifiers is inevitable in the operating room making radiation in the operating environment unavoidable. The risk to patients and staff can be easily reduced by adhering to the central principles of the ICRP recommendations: instill awareness among the healthcare workers, understand risks of working in a controlled area, understand individual responsibilities, and practice correct behavior; last but not least, understand the radiation protection measures available in your work setting. 1.6.2.3 Further reading Sutherland AG, Finlayson DF (1998) Screening times with image intensifier in orthopaedic trauma surgery. J R Coll Surg; 43:265 266. Devalia KL, Guha A, Devadoss VG (2004) The need to protect the thyroid gland during image intensifier use in orthopaedic procedures. Acta Orthop Belg; 70(5):474 477. International Commission on Radiological Protection (1990) Recommendations of the International Commission on Radiological Protection. No. 60:21:72 79. The Department of PET and Nuclear Medicine at Royal Prince Alfred Hospital (2001) Introduction to radiation protection, dose limits and dose constraints, radiation and dose measurement, effects of radiation on humans, the system of radiation protection protocol, radiation safety and personal protection in diagnostic radiology. In: Personal Dosimetry, Revised. The University of Iowa, Health Protection Office, Diagnostic X-Ray Procedures (2003) Radiation Safety Training Program, Revised. US Environmental Protection Agency (2004) Understanding Radiation, Ionizing and Non-Ionizing Radiation. Washington, DC: EPA. US Nuclear Regulatory Commission (2005) What is radiation? www.nrc.gov. US Nuclear Regulatory Commission (2003) How can exposure to radiation be minimized? www.nrc.gov. 92 Techniques and Principles for the Operating Room Porteous, Bäuerle PORP_Book.indb 92 5/7/10 11:15:53 AM