Radiation Protection PDF

# Radiation Protection A goal in diagnostic radiology is to obtain maximum diagnostic information with minimal radiation exposure of the patient, radiology personnel, and general public. This is achievable if guidelines for safe practice are followed and personal protective equipment (PPE) is used....

# Radiation Protection A goal in diagnostic radiology is to obtain maximum diagnostic information with minimal radiation exposure of the patient, radiology personnel, and general public. This is achievable if guidelines for safe practice are followed and personal protective equipment (PPE) is used. However, because x-rays cannot be seen or felt, it is easy to disregard the danger associated with occupational x-ray exposure (Fig. 1.4). Many veterinarians and technologists have developed a cavalier attitude regarding the hazards associated with ionizing radiation and put themselves at risk, from both medical and legal perspectives. While the use of digital radiograph has vastly improved radiographic quality in veterinary imaging, it has also in many instances led to further disregard for safe radiation practices since the cost and time investment in retakes are minimal. General principles of radiation protection that can form the basis of a safe workplace are discussed in this chapter. Any specific recommendations regarding radiation safety or protection made in this chapter are subject to overrule by local, state, and/or federal regulations. ## Careless and Unacceptable Approach to Radiography _Fig. 1.4 Careless and unacceptable approach to radiography. The technologist's hands are in the primary x-ray beam. Careless habits such as this are perpetuated because of the stealthy properties of x-rays and lead to unnecessary personnel exposure that could become biologically significant._ The image shows a technologist's hand inside of the primary x-ray beam during a radiography procedure. ## Radiation Units Two related concepts must be understood before radiation units are considered. First, **radiation exposure** and **radiation absorption** are not the same. Some tissues absorb radiation more effectively than others, meaning that exposure to the same amount of radiation will result in different absorbed doses in these tissues. Second, the biologic effect of the same absorbed dose can also be different, being a function of both radiation type and energy. A numeric weighting factor or **quality factor** has been derived to estimate the difference in biologic effectiveness of various types of radiation (Table 1.2). ## Radiation Weighting Factor (Quality Factor) for Various Radiation Types | TYPE OF RADIATION | WEIGHTING FACTOR | | ---------------------- | ------------------ | | X-rays | 1 | | Gamma rays | 1 | | Beta particle (electron) | 1 | | Neutrons | | | <10 keV | 5 | | 10-100 keV | 10 | | 100 keV-2 MeV | 20 | | Alpha particles | 20 | ## Radiation Exposure Radiation exposure, radiation absorption, and dose equivalent each have their own unit of measure that was defined originally in the centimeter-gram-second (CGS) system of measures. In 1977, the International System of Units (SI units) was developed in keeping with the trend toward universal adoption of the metric system (Table 1.3). In general, the system of SI units has not been universally adopted in the United States, and CGS radiation units are still used, which can be a source of confusion. ## Exposure Radiation exposure is based on the amount of ionization in air that the radiation produces and is quantified by the amount of electrical charge resulting from the ionization. Radiation exposure is expressed in the SI system as coulombs per kilogram of air (C/kg) (see Table 1.3). This SI unit of exposure is cumbersome; thus, an older term of exposure, the roentgen, is still used. One roentgen equals a charge of 2.58 C/kg in air. ## Radiation Units | QUANTITY | CGS UNIT | VALUE | SI UNIT | VALUE | | ------------------------ | ------------ | ------------------------------------------------------------------------------------------ | ------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Exposure dose | roentgen | One electrostatic unit of electricity in 1 cubic centimeter of dry air at 0°C and standard atmospheric pressure 100 ergs/g of tissue | roentgen* | 2.58 × 10^-4 C/kg | | Absorbed dose | rad | 100 ergs/g of tissue | gray (Gy) | 1 Gy = 1 joule/kg (1 Gy = 100 rads) | | Equivalent biologic dose | rem | Dose in rads times weighting factor | sievert (Sv) | Dose in Gy times weighting factor (1 rem = 10 mSv) | ## Absorbed Dose The efficiency of x-ray absorption in different materials can vary widely. For example, lead is a much more efficient absorber than water. Therefore, the radiation dose in tissues with different absorption efficiencies will be different when exposed to the same amount of radiation (Fig. 1.5). The SI unit for absorbed dose is the **gray (Gy)**. One **gray** is the amount of radiation leading to absorption of 1 joule/kg of tissue. Before SI units were accepted, the unit of absorbed dose was the **rad**, which is equal to 100 ergs/g of tissue (see Table 1.3). The term **rad** is obsolete, but it is so engrained in the radiology lexicon that it has not been replaced universally by the Gy. One gray is equal to 100 rad. ## Two Materials Exposed to the Same Number of X-Ray Photons _Fig. 1.5 Two materials are exposed to the same number of x-ray photons, represented by the arrows at the top. Thus, the exposure dose, in roentgens, or in coulombs per kilogram, is the same for both materials. However, the efficiency of x-ray absorption for the two materials is different. The material on the left is more efficient in absorbing x-rays than the material on the right. Therefore, the absorbed dose will be higher in the material on the left even though the exposure dose is the same. One real-life example of this phenomenon is a limb, where bone would be the high-efficiency absorber and fat or muscle the low-efficiency absorber._ The image shows two rectangles, labeled "High Efficiency Absorber" and "Low Efficiency Absorber." Both have arrows pointing downwards that represent X-Ray photons. The High Efficiency absorber has more arrows coming out the bottom of the rectangle, representing a higher absorbed dose because of more absorption and fewer transmitted photons, while the Low Efficiency absorber has fewer photons coming out the bottom, representing a lower absorbed dose because of less absorption and more transmitted photons. ## Exposure to Bone In soft tissue such as muscle, exposure to 1 roentgen amounts to an absorbed dose of approximately 0.9 centigray (cGy) or 0.9 rad. In comparison, bone is a more efficient absorber of x-rays than soft tissue, and exposure to bone of 1 roentgen results in a higher bone-absorbed dose. This difference in absorption between bone and soft tissue may be as great as a factor of 4-5 with low-energy radiation. Differential x-ray absorption between various tissues is the basis of radiographic contrast, and without this difference making a meaningful radiograph would not be possible. As discussed later, the magnitude of the difference between exposure and absorbed dose is the greatest for low energy photons and decreases as photon energy increases. ## Dose Equivalent As noted earlier, the same absorbed dose, in Gy, from different types of radiation may not produce the same biologic effect. For example, damage from particulate radiation, such as an alpha particle is greater on a Gy-for-Gy basis than damage from the same dose of x-rays (see Table 1.2). This is related to differences in ionization density for different types of radiation. A large, heavily charged particle, such as an alpha particle, creates many ionizations that are close together compared to a small lightly charged particle, such as an electron, where ionizations are more widely spaced (Fig. 1.6). The closer the ionizations are to each other, i.e., greater ionization density, the more biologic damage results from a given dose. Therefore, deposition of 1 Gy from an alpha particle does more biologic damage than deposition of 1 Gy from an x-ray because the ionizations are more clustered. The difference in biologic damage from the same absorbed dose of various radiation types is estimated by the weighting factor, as described earlier (see Table 1.2). In the SI system, the unit of dose equivalency is the sievert (Sv); the Sv is derived from the product of the absorbed dose in Gy and the weighting factor. Before SI units were accepted, the unit of dose equivalency was the radiation equivalent in man or rem (see Table 1.3). The rem was derived from the product of the absorbed dose in rads and the weighting factor, because 1 Gy = 100 rads, 1 Sv = 100 rem. ## Ionization Density Along Paths of X-Ray and Alpha Particle _Fig. 1.6 Representation of the ionization density along the paths of an x-ray and an alpha particle. The ionization density along the path of the alpha particle is much higher because of its large mass and 2+ charge. This will lead to greater biologic damage on a Gy-per-Gy basis, and a correction factor will be needed to compare the biologic damage resulting from equal absorbed doses of x-rays versus alpha particles._ The image shows two lines. The top line has a few scattered asterisk-like marks on it, representing ionizations along the path of an x-ray. The bottom line has a large number of asterisk-like marks clustered together along the path of an alpha particle, representing a higher ionization density than an x-ray. ## Radiation Safety Principles of radiation safety are based on establishment of guidelines to prevent unnecessary exposure of radiation workers and the general public to ionizing radiation. The premise of radiation protection is that some low level of radiation exposure to radiation workers is permissible and will not lead to significant abnormalities or disease. Adverse effects can be classified as either deterministic or stochastic. Deterministic effects have a threshold. In other words, below some dose there is no effect, but above the threshold dose the severity of the effect is dose related. Radiation-induced cataracts are an example of a deterministic effect. Conversely, stochastic (random) effects have no dose threshold, and the severity of the effect is independent of dose. Radiation-induced cancer is an example of a stochastic effect. ## Maximum Permissible Dose Maximum permissible dose (MPD) is the maximal amount of absorbed radiation that can be delivered to an individual as a whole-body dose or a dose to a specific organ and still be considered safe. The term safe in this context means that there is no conclusive evidence that the MPD will lead to harmful immediate or long-term effects to the body as a whole or to any individual structure or organ. Although the effect of very low doses of radiation is not known with certainty, it is safe to assume that any amount of radiation will have some effect and keeping one's dose below the MPD is important. An analogy could be made to smoking a cigarette once a month. There is no evidence that physical damage results from this frequency of smoking, but with increased smoking the probability of physical damage escalates by virtue of a cumulative effect. Unfortunately, an absolute threshold below which damage will definitely not occur has not been established for either cigarette smoking or radiation exposure. ## Radiation Exposure Guidelines and Bureaucracy There are multiple levels of bureaucracy regarding the establishment of guidelines for radiation exposure, aimed at avoiding deterministic and stochastic effects. Understanding the mission of all involved organizations can be confusing. Furthermore, different exposure limits are defined for radiation workers versus the general public. These exposure limits vary according to risk versus benefit. For example, the small risk to a member of the general public from being subjected to a radiographic study is outweighed by the benefit of a diagnosis. Likewise, the slightly higher exposure limits allowed for radiation workers are considered acceptable with respect to the missions of the occupation. ## International Commission on Radiological Protection (ICRP) The International Commission on Radiological Protection (ICRP) is the primary international body focusing on protection against ionizing radiation. The ICRP is an independent, international, nongovernmental organization. The ICRP provides recommendations and guidance on protection against the risks associated with ionizing radiation. Their recommendations are published approximately four times each year as the journal Annals of the ICRP. The whole-body limit for radiation workers set by the ICRP for avoiding stochastic effects is 20 millisievert (mSv) per year, averaged over 5 years, with the provision that dose in any one year should not exceed 50 mSv. The ICRP maintains exposure per quarter should not exceed 12.5 mSv. ## National Council on Radiation Protection (NCRP) In the United States, the National Council on Radiation Protection (NCRP) was chartered by Congress in 1964. Some of the objectives of the NCRP are to develop recommendations about radiation protection and to cooperate with the ICRP. The whole-body limit set for radiation workers by the NCRP for avoiding stochastic effects is 50 mSv per year with a lifetime accumulation not to exceed 10 mSv × age in years. The NCRP also recommends that no occupational exposure occur until the age of 18 years. ## Nuclear Regulatory Commission (NRC) The Nuclear Regulatory Commission (NRC) is the agency officially responsible for defining federal exposure standards in the United States. The NRC has adopted the annual radiation dose to adult radiation workers as recommended by the NCRP, a maximum of 50 mSv (5 rem) per year. However, the NRC has not established an upper limit for cumulative exposure because of the uncertainty of such predictions. The difference in opinion between the NRC and the NCRP regarding the limits for cumulative exposure can be confusing. However, rather than focusing on a specific number for cumulative or annual exposure, the goal should be to minimize any exposure. This is the basis of the ALARA approach, discussed later. ## Radiation Limits for Pregnant Women The allowable limit for radiation workers who become pregnant is lower than for nonpregnant radiation workers but ideally should be zero. The monthly exposure limit for the embryo or fetus should not exceed 0.5 mSv (0.05 rem). It is the responsibility of the pregnant radiation worker to notify the supervisor of the pregnancy in writing so that any change in work habits needed to stay within the recommended dose limit can be implemented. For the general public, radiation exposure, excluding that related to medical use such as diagnostic imaging and radiation therapy, should not exceed 1 mSv (0.1 rem) per year. ## Natural and Man-Made Radiation Exposure In addition to occupational exposure of radiation workers, the entire population is exposed continually to very low levels of natural and man-made radiation. A revised breakdown of relative exposure of the U.S. public to radiation by various sources was published by the NCRP in 2015 (Fig. 1.7). Revised estimates were needed because in 2006, Americans were exposed to more than seven times as much ionizing radiation from medical procedures as in the early 1980s, mainly due to increases in CT imaging. The number of CT studies performed in human patients doubled between 1997 and 2006. In 2006, medical exposure constituted nearly half of the total radiation exposure of the U.S. population from all sources. The next largest contributor to population exposure was background radiation, mainly from radon gas. The relative level of background radiation varies with geographic location. For example, exposure to cosmic radiation increases at higher elevations, and household radon exposure is greater in the eastern United States. In general, these types of radiation exposures are not considered harmful, providing the use of medical imaging is monitored. The United States Environmental Protection Agency (EPA) provides a calculator that allows estimation of your yearly dose from the most significant sources of ionizing radiation ## Sources of Radiation Exposure in the United States _Fig. 1.7 An estimate of sources of exposure dose from ionizing radiation in the United States. (With permission of the National Council on Radiation Protection and Measurements, http://NCRPonline.org.)_ The image is a pie chart of percentages representing sources of radiation exposure in the United States. The following are listed in order of percentage, from highest to lowest. 1. Radon and thoron: 37% 2. Medical imaging: 36% 3. Nuclear medicine: 12% 4. Internal: 5% 5. Cosmic: 5% 6. Terrestrial: 3% 7. Consumer products: 2% 8. Industrial and occupational: 0.1% ## Practical Considerations Technologists assuming the role of radiation workers in veterinary practices must be aware of the risks of radiation. They should be trained in patient positioning for radiography and should be proficient in equipment operation. Technologists should be instructed on the proper use and care of PPE such as lead-impregnated aprons and gloves, and how to adhere to the ALARA (as low as reasonably achievable) principle. The variables used in adhering to ALARA are distance, time, and shielding. ## Distance The distance between personnel in the room and the x-ray tube should be as great as possible because distance is one of the most effective ways of reducing dose. Exposure dose does not change linearly with distance but is dependent on the square of the distance. For example, doubling the distance reduces exposure by a factor of 4, not by a factor of 2. Holding cassettes by hand for equine radiography is discouraged because this can place the employee in the primary beam. Handholding of portable x-ray machines for radiography of the equine distal limb is safe, as long as the machine is adequately shielded. Handholding of companion animals for radiography is permissible, but body parts should be as far from the primary x-ray beam as possible and no part of the body should ever be in the primary beam, regardless of whether protective aprons and gloves are used. With the use of chemical restraint, tape, and sandbags for positioning, it is often possible for the technologist to exit the room during the exposure. Some state veterinary practice acts stipulate that the technologist cannot be in the room during the exposure. ## Beam Collimation Effective use of beam collimation is another component of distance as this further increases the distance of the technologist from the primary x-ray beam, and also reduces scattered radiation. However, failure to properly collimate the primary x-ray beam is a major error in veterinary radiology. Digital software also allows the visibility of unprotected hands in an image to be cropped out of view (Fig. 1.8). ## Ventrodorsal View of a Canine Pelvis _Fig. 1.8 A, Ventrodorsal view of a canine pelvis with worker's ungloved hand holding patient's pelvic limbs. B, Dashed line shows application of software cropping tool. C, Cropped image is ready to send to workstation. Daily repetition of this hazardous practice leads to continued overexposure of the hands and wrists, increasing the risk for squamous cell or basal cell carcinomas._ The image shows three different x-ray images. * A: Ventrodorsal view of a canine pelvis with worker's ungloved hand holding patient's pelvic limbs. * B: Dashed line shows application of software cropping tool. * C: Cropped image is ready to send to workstation. ## Time Time is directly related to the number of images created. Time can be minimized by using sedation or anesthesia for uncooperative patients, or for complicated examinations such as spine or skull studies. Rotation of the technical staff through the radiology service will also dilute any exposure over a larger pool, leading to reduction in individual exposure levels. Retake examinations also increase personnel dose, and these have likely increased with the increase in digital imaging as retakes are less labor intensive. ## Shielding State building codes require structural shielding to protect personnel and the general public, such as clients in the waiting or examination rooms, from unnecessary radiation exposure. The specific details regarding requisite structural shielding can be obtained from the state radiation protection office. ## Radiation Protection Equipment The most effective PPE for radiation workers is lead-impregnated aprons, gloves, thyroid shields, and eyeglasses. Protective aprons and gloves designed for use in the x-ray room are usually 0.5 mm Pb equivalent. Unfortunately, this equipment is not used consistently. When apron and glove use was monitored in a university setting with video cameras, gloves were used properly in only 46.3% of the studies and leaded eyeglasses were worn only 1.7% of the time. PPE use was also found to be deficient in equine practice. Although not documented, glove use is almost certainly inadequate in private small animal practice (Fig. 1.9A; see Fig. 1.4). More commonly, when lead gloves are not used, the technologist attempts to keep the unshielded hands outside of the primary beam, thinking that the collimator eliminates radiation exposure in this area. This is not true. There is always enough scattered radiation outside the primary beam to capture an image of parts of the patient or technologist in that area, and this also leads to unnecessary personnel exposure (see Fig. 1.9B). Additionally, the hand will frequently end up in the periphery of the primary beam, leading to even higher exposure. In fact, in Fig. 1.9B the tip of a finger (white arrowhead) is in the edge of the primary beam, but the fingertip is not visible because of overexposure. Another common mistake is the belief that because lead aprons and gloves are very heavy, they can be used to shield body parts within the primary beam (see Fig. 1.9A). This is also not true. Lead aprons and gloves are designed solely for protecting against scattered radiation and must never be placed in the primary beam because they do not entirely attenuate the x-ray beam. Covering a hand in the primary x-ray beam with an apron or glove is not adequate protection, and the hand will receive unnecessary, excessive radiation (see Fig. 1.9C). The effects of scattered photons from the floor of the x-ray room, or x-ray table, are also usually ignored, but these are important sources of scattered radiation (see Fig. 1.9D). Lastly, radiation protection mittens with a slit in the palm are available. Extending the fingers through the slit facilitates positioning but reduces the amount of overlying protective lead material and leads to excessive extremity dose whether the hand receives primary or secondary radiation. Aprons and gloves should be placed on racks when not in use. This decreases the risk of creasing and folding that lead to cracking or separation of the protective lead layering. Use of a glove rack also facilitates the evaporation of perspiration that reduces odor. Aprons and gloves should be inspected visually on an annual basis, and any portion that appears physically damaged should be evaluated radiographically for evidence of a crack. ## Examples of Poor Radiation Safety Practice. _Fig. 1.9 Examples of poor radiation safety practice. A, Hands were placed in the primary beam to position this small patient. Although gloves were used, they are not adequate for shielding against the primary x-ray beam and the hands will receive an unacceptable dose. B, Dorsoventral skull radiograph of a dog. A sandbag is being used to secure the neck. The technologist is not wearing lead gloves and has grasped the ears of the dog, which are outside of the primary beam, to keep the head in the proper position. The dog's right ear can be seen (black arrow). On the left side, the technologist's fingers can also be seen (white arrow), because of exposure from radiation outside of the primary beam. The tip of a finger is also in the primary beam (white arrowhead). A portion of the technologist's hand can also be seen on the dog's right side, peripheral to the dog's ear but not to the extent that it is identifiable as a hand. The most rostral portion of the dog's nose is also visible outside of the primary beam. C, A lateral radiograph of a canine skull was being made. The technologist held the ears in the primary beam with an unprotected hand and then covered their hand with a lead apron, thinking the apron would attenuate the x-rays. It did not. The bones in the technologist's hand are clearly visible (black arrows) because of x-rays penetrating the apron. D, A small patient is being restrained by an unprotected hand but a lead glove is placed on top of the hand, similar to the situation illustrated in part C of this figure. As already stated, this is ineffective because many of the oncoming high-energy photons will penetrate the glove and strike the hand. Also, photons penetrating the cassette and table will strike the floor and be scattered back, also striking the hand. Radiation backscatter is also a reason that the technologist should not sit on the edge of the x-ray table while restraining a patient for radiography. In that instance the scattered photons are going to strike a body part or parts that are more revered than a hand._ The image shows four different x-ray images. * A: Hands were placed in the primary beam to position this small patient. Although gloves were used, they are not adequate for shielding against the primary x-ray beam and the hands will receive an unacceptable dose. * B: Dorsoventral skull radiograph of a dog. A sandbag is being used to secure the neck. The technologist is not wearing lead gloves and has grasped the ears of the dog, which are outside of the primary beam, to keep the head in the proper position. The dog's right ear can be seen (black arrow). On the left side, the technologist's fingers can also be seen (white arrow), because of exposure from radiation outside of the primary beam. The tip of a finger is also in the primary beam (white arrowhead). A portion of the technologist's hand can also be seen on the dog's right side, peripheral to the dog's ear but not to the extent that it is identifiable as a hand. The most rostral portion of the dog's nose is also visible outside of the primary beam. * C: A lateral radiograph of a canine skull was being made. The technologist held the ears in the primary beam with an unprotected hand and then covered their hand with a lead apron, thinking the apron would attenuate the x-rays. It did not. The bones in the technologist's hand are clearly visible (black arrows) because of x-rays penetrating the apron. * D: A small patient is being restrained by an unprotected hand but a lead glove is placed on top of the hand, similar to the situation illustrated in part C of this figure. As already stated, this is ineffective because many of the oncoming high-energy photons will penetrate the glove and strike the hand. Also, photons penetrating the cassette and table will strike the floor and be scattered back, also striking the hand. Radiation backscatter is also a reason that the technologist should not sit on the edge of the x-ray table while restraining a patient for radiography. In that instance the scattered photons are going to strike a body part or parts that are more revered than a hand. ## Radiation Supervisor Identifying a member of the technical staff as a radiation supervisor will optimize the quality of images produced and minimize occupational radiation dose. Having a dedicated radiation protection supervisor provides the technologist with ownership in the process, which will increase quality. The continuity of supervision will contribute to a steady stream of high-quality images and low personnel exposure readings. The following are some reasonable responsibilities of a radiation supervisor: * Establish and supervise the implementation of written operating procedures for all employees involved with radiography. * Periodically review procedures to ensure conformity with local regulations. * Instruct all personnel in proper radiation protection practices and in efficient and safe equipment operation. * Oversee conduction of required radiation surveys and keep records of such surveys and tests, including summaries of corrective measures recommended or instituted. * Routinely observe and periodically test interlock switches and warning signals. * Ensure that warning signs and signals are properly located. * Ensure that all equipment is maintained in top-notch working order. Perform annual evaluation of radiation protection equipment. * Determine the cause of each known or suspected case of excessive abnormal exposure and take steps to prevent its recurrence. * Train staff in proper radiographic positioning and restraint procedures. * Radiation safety seminars should be held on a yearly basis to ensure compliance and to educate new personnel. ## Personnel Dose Monitoring Personnel dose monitoring is used to check the adequacy of the radiation safety program, disclose improper radiation protection practices, and detect potentially serious radiation exposure situations. A radiation dosimetry badge is the most commonly used personnel monitoring device. A radiation badge consists of a plastic holder, measuring approximately 2 to 3 cm on a side, which has a clip allowing it to be secured to clothing. Modern radiation badges contain either radiation-sensitive aluminum oxide or lithium fluoride crystals. These compounds trap electrons energized by oncoming radiation, and the number of trapped electrons can be quantified and related to the amount of exposure. Radiation badges should be analyzed at least quarterly, but a monthly analysis is preferable so that exposure problems are detected sooner. Badges for declared pregnant workers should be analyzed monthly. Personnel dose monitoring should be performed in controlled areas for each occupationally exposed individual who has a reasonable possibility of receiving a dose exceeding 10% of the applicable MPD. The radiation badge must be worn only in the workplace and never when the person is exposed to ionizing radiation as part of his or her own medical or dental examinations. The badge is intended to monitor occupational radiation exposure and not medical exposure. If the badge is worn outside of the workplace erroneous readings can result. The radiation badge should be worn on the upper or lower torso. When a protective apron is worn, the radiation badge should be on the outside of the apron for monitoring the radiation environment, but a second radiation badge may also be worn inside the apron when an estimate of body exposure is desired. Anyone occupationally exposed to radiation should have their own badge and radiation badges should never be shared. ## Basic Radiation Safety Rules for Diagnostic Radiology The basic radiation safety rules for diagnostic radiology are: * Only personnel necessary to complete the procedure should be in the x-ray room at the time of exposure. * Persons younger than 18 years and pregnant women must not be in the x-ray room during the examination. * Personnel who assist with radiographic examinations should have a rotating duty roster to minimize exposure to any one person. * Sandbags, sponges, tape, or other restraining devices should be used for positioning the patient rather than manual restraint. * Anesthesia or sedation should be used, when possible, to facilitate patient restraint. * No part of the technologist should be in the primary beam, whether or not protected by gloves or aprons. * Protective aprons should always be worn when positioning an animal. * Protective gloves should be worn if hands are near the primary beam. * Protective glasses should be worn if the work level is heavy or when radiographing large animals. These glasses provide 0.25 mm Pb equivalent protection to the lens. * Thyroid shields should always be worn. These are “mini-aprons" that are worn around the neck to protect the thyroid gland. * The primary beam should be collimated so each image has an unexposed border, proving that the primary beam does not exceed the size of the cassette or imaging plate. * All personnel involved with patient radiography should wear a radiation badge during working hours. * The radiographic procedure should be planned carefully, and the machine settings double-checked prior to exposure.