Basic Considerations of
Radiation Safety and Barrier Protection

Radiation Exposure No amount of radiation can be considered safe for living matter. Even low-dose exposures of radiation can negatively impact human tissue; however, repair mechanisms probably make most of these effects inconsequential. Greater exposure to radiation implies greater risk for carcinogenesis.6 Evan C. Lipsitz, MD, Assistant Professor of Surgery, Montefiore Medical Center, New York, Division of Vascular Surgery, says "We should remember that radiation exposure is cumulative over one's lifetime and that the effects are permanent. And, reducing fluoroscopy time, increasing distance from the source, and using adequate protection with monitoring are the basic methods of reducing exposure."7 POSSIBLE BIOLOGICAL EFFECTS Biological effects of radiation can be separated into two categories: Deterministic effects and stochastic effects. Deterministic effects are those for which a minimum number of cells must be affected above a threshold before a biological response is seen. Cataracts or radiation-induced erythema and necrosis are examples of deterministic radiation effects. As the dose increases above the threshold, the likelihood of seeing the effect and the severity of the effect increases. If the dose is sufficient, there is a 100% certainty the effect will be induced.8 Many radiation-induced effects occur when change in a single cell is sufficient to initiate biological processes such as the development of cancer. These effects are called stochastic and no known threshold dose exists. The likelihood of inducing the effect increases with dose and may differ among individuals. Such radiation risks include cancers of the blood, bone, lung, parotid gland, and other organs, including the skin. The first cancer thought to be caused by exposure to x-rays was a skin cancer case diagnosed in 1902 - seven years after Röntgen's discovery. Again, early radiologists were not aware of the risks associated with exposure to x-rays, and many accumulated very high radiation doses in a short time.9 If fluoroscopic doses are sufficiently high to include deterministic effects, skin effects are one of the earliest and most frequently observed signs. Skin exposed to ultraviolet radiation is more sensitive to x-rays. This is because fluoroscopic x-rays are attenuated rapidly in tissue. The dose is maximized at the point where the radiation beams enter the skin. The skin is also rendered susceptible to radiation effects because basal cells of the epidermis divide rapidly. Rapidly dividing stem cell populations contain "new" skin cells, and these immature cells are typically more sensitive to radiation than mature cells. The most common forms of cancer on the hands and arms are squamous cell carcinomas, while basal cell carcinomas are more likely to occur on the head and neck. Radiogenic skin cancer is frequently associated with chronic dermatitis, sometimes only observable at the microscopic level. As GT Nahass writes in the Journal of the American Academy of Dermatology (1997), since the signs of acute radiodermatitis clear spontaneously, cases with mild symptoms may go unrecognized and untreated. The long-term consequences of acute radiodermatitis often appear months to years later. Radiation leukemia generally develops 10-15 years after exposure, but may occur as early as two years or as late as 25 years. The latent period for radiogenic skin cancer ranges from 4 to 40+ years, with squamous cell and basal cell carcinomas being the main associated cancer types. DOSE LIMITS AND MONITORING Since radiation dose is cumulative, the NRC and state regulatory agencies mandate the use of wearable radiation monitors (film badges) while performing fluoroscopic procedures. These devices respond to radiation exposure by eliciting a signal that indicates an estimate of the accumulated exposure over a period of time. The International Commission on Radiological Protection (ICRP) sets effective radiation dose limits. Effective dose is a concept proposed by the ICRP to relate the risk from partial-body radiation dose to that from an equivalent whole-body dose. The ICRP suggests that approximately 37% of the total skin surface not shielded by a lead apron is present in the arms, lower legs, hands, and feet, with skin of the hands and forearms most likely to receive a higher radiation dose than the skin areas measured by the dosimeter (radiation monitor) placed over the collar of the lead apron.10 If the monitor is worn under the apron, the dose to the head and neck will be unknown, and this is unacceptable. Unfortunately, there is no precise way of determining how much exposure one has had without diligently wearing some form of monitor. Practitioners with significant exposure - such as in the cardiac catheterization laboratory - wear monitors inside the lead apron, external monitors, and ring monitors on the fingers. However, if fluoroscopy is only being used sporadically, a pocket dosimeter may offer ample monitoring. DOSE LIMITS FOR ADULT WORKERS 2,000 millirem (20 mSv) per year averaged over a five-year period - not to exceed 5,000 millirem or 50 mSv in any one year.11 15,000 millirem (150 mSv) per year to the lens of the eye.12 50,000 millirem (500 mSv) per year to the skin or to any extremities - hands, forearms or feet, and ankles.11 The annual effective whole-body dose limit for physicians is 50 mSv.13 Scatter radiation is a major concern for individuals in a fluoroscopy suite. Scatter can come from any direction and can increase when imaging denser tissues. Since the main source of scatter radiation is from both the imaging equipment and the patient, standing as far away as possible from the imaging unit and the patient will reduce one's exposure. However, as soon as the x-ray switch is disengaged, x-rays cease to exist in the room and neither the machine nor the patient are sources of scatter radiation. PROTECTIVE SHIELDING There is no law mandating the use of shielding devices commonly used in practice today (i.e., lead aprons, radiation attenuation gloves, thyroid shields, or protective eyewear). However, using these devices has become a standard and essential part of functioning in a fluoroscopic environment, even for individuals receiving less than 50 mSv per year. Protective apparel is particularly important during mobile C-arm fluoroscopy or portable radiography since the control console is not positioned behind fixed protective barriers. When using fixed units, personnel may leave the room while screening runs are obtained. Because this is not possible with portable radiography systems, drapes and aprons made of lead-impregnated vinyl are the primary protective barriers against stray radiation. Well-placed drapes can provide medical staff some additional protection by reducing radiation scatter.14 "Wrap-around" lead aprons are useful when there is a great amount of time spent turned away from the patient for protection of the back of the body. Legs located near the x-ray tube must be shielded as well. Thyroid shields are often overlooked but can minimize the possibility of thyroid cancer.15 These devices enhance protection to the thyroid but can impede maneuverability. As with other types of optional protection, there is a trade-off between greater protection and freedom of motion. Pregnant women may continue to work in fluoroscopic areas, but they should wear an extra radiation monitor at the level of the abdomen underneath the lead apron. This serves as a monitor for the dose to the conceptus. Specially designed lead maternity aprons are also available to provide added protection.

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