Radiation Safety and Protection

Function

A basic understanding of the science behind the damaging effects of radiation is crucial in evaluating the different strategies to protect medical professionals and patients. X-rays are composed of high-energy photons within the electromagnetic spectrum. X-rays are notable in comparison to lower energy photons since they are powerful enough to break molecular bonds and ionize atoms.[4] This ionization produces free radicals, chemically active compounds that can indirectly damage DNA.[5] Medical staff and patients can be exposed to x-ray radiation either as scattered x-rays or by direct exposure to the x-ray beam. Scattered x-rays give up part of their energy during the scattering process, and thus energy deposited in tissues from scattered x-rays is lower than directly from the x-ray source. Radiation doses can be expressed in three different ways. The absorbed dose is the radiation deposited in an object and is measured in milligrays (mGy). The equivalent dose is calculated, taking into account the organ-specific radiation exposure, as well as the organ's sensitivity to radiation, and is expressed in millisieverts (mSv). The effective dose is the sum over the entire body of the individual organ equivalent doses and is expressed in millisieverts (mSv). An understanding of these definitions is critical to interpreting dose recommendations. The ICRP's dose recommendations are shown in fig 1.[3] For reference, 20 mSv/year roughly equates to 2 to 3 abdominal and pelvic computed tomography (CT) scans or 7 TO 9 years of background radiation. Exposure surpassing this threshold averaged over five years has been associated with a 1 in 1000 lifetime risk of fatal cancer.[6][7][5]

Issues of Concern

Radiation exposure can produce biological effects as either a dose-dependent effect or a dose-dependent probability.[8] Dose-dependent effects are referred to as deterministic effects and occur when a specific exposure threshold has been exceeded. A dose-dependent probability is referred to as a stochastic effect and represents an outcome that occurs with a certain probability but without a defined threshold at which these effects are triggered.[9] Examples of deterministic effects that have been documented in the fields of interventional radiology, cardiology, and radiation treatment include radiation-induced thyroiditis, dermatitis, and hair loss.[10] Stochastic effects are discovered many years after radiation exposure and include the development of cancer.[3] It is important to note that deterministic effects are determined by the cumulative amount of radiation exposure an organ or tissue experiences over time (the lifetime equivalent dose). In comparison, there is a chance that a specific x-ray causes DNA damage that later develops into cancer, a stochastic effect. As the number of x-rays a patient is exposed to increases, the chance of a stochastic effect increases; however, the lifetime equivalent radiation dose does not play a role in stochastic effects. Researching the effects of long-term low-dose exposure to ionizing radiation is difficult because literature is based on epidemiologic data from large radiation exposures at doses that are much higher than is used in the medical setting. Current literature suggests that medical radiation may result in a modest increase in the risk of cataracts, cancer, and possibly hereditary diseases.[6] 

Clinical Significance

The duration of radiation exposure, distance from the radiation source, and physical shielding are the key facets in reducing exposure. The exposure duration can be minimized in several ways. When exposing a patient to radiation, the technician or physician should preplan the required images to avoid unnecessary and redundant exposure. Magnification significantly increases the exposure to the patient; therefore, magnification should be used judiciously.[11] Continuous or live fluoroscopy may be helpful to understand anatomy during procedures better, but standard fluoroscopy machines capture roughly 35 images per second. Decreased exposure can be achieved instead by using pulsed fluoroscopy, which obtains about five images per second without sacrificing imaging quality. Lastly, exposure duration should be limited whenever possible. 

Increasing the distance between the x-ray beam and the part that is being imaged is another way to minimize exposure. The image intensifier or x-ray plate should be as close to the patient as possible, with the x-ray tube positioned as far away as possible while maintaining adequate image resolution. A similar approach can be used to minimize exposure to medical professionals. Scattered radiation—the type of radiation that surgeons, interventionalists, and operating room staff commonly encounter during procedures requiring fluoroscopy—follows an inverse square law. Scattering exposure levels decrease proportionally with the inverse of the distance squared from the x-ray source. Staff can lower their exposure levels by a factor of four by doubling their distance from the source. Through this simple concept, occupational radiation exposure can be dramatically reduced.

Physical radiation shielding can be accomplished with different forms of personal protective equipment (PPE). Some fluoroscopy suites contain ceiling-suspended lead acrylic shields, which can reduce doses to the head and neck by a factor of 10. Portable rolling shields, which do not require installation, can protect staff in operating rooms and interventional settings. These mobile shields have been shown to decrease the effective radiation dose to staff by more than 90% when used correctly.[12] In cases where it is not feasible to shield oneself behind a physical barrier, all personnel should wear leaded aprons for protection. Leaded aprons, which are required in most states, commonly come in thicknesses of 0.25 mm, 0.35 mm, and 0.5 mm. Aprons that wrap circumferentially around the body are preferred to front aprons, given their increased surface area coverage. In general, transmission through leaded aprons is typically between 0.5% and 5%. Leaded aprons should always be companied by a thyroid shield. Personal protective equipment also protects our patients. Patients should wear protective gowns in areas not being imaged, whether in plain radiographs, fluoroscopy, or CT scans. Leaded eyeglasses and should be at least 0.25 mm lead equivalents to provide adequate protection for the lens of the eye. Leaded glasses are commonly cited as the least worn piece of PPE in multiple studies, with compliance rates ranging from 2.5% to 5%.[13] Studies have shown a relationship between occupational radiation doses and cataract development before 50 in a large cohort of radiation technologists, specifically the posterior lens.[14] Interestingly, the opacification of the posterior lens, in comparison to the other locations, is relatively specific to radiation exposure. Regular use of leaded eyeglasses can reduce radiation exposure to the lens by 90%. The low compliance rate for wearing leaded eyeglasses demonstrates an area for improvement. Beyond the appropriate use of leaded aprons, proper storage and testing of the equipment are critical to ensuring its effectiveness. Lead garments should be checked every six months to assure their integrity, and leaded aprons should be hung rather than folded to prevent cracking.

Dosimeters are devices that measure cumulative radiation exposure. These devices should be worn by all hospital staff who encounter planned ionizing radiation. Unfortunately, in a significant number of healthcare settings, there is a paucity of monitoring and, thus, a lack of reliable data. Sanchez et al. reported that as much as 50% of physicians do not wear or incorrectly wear dosimeters.[15] Dosimeters should be worn both outside and inside the leaded apron for comparison of doses, and the readings should be analyzed by the facility’s radiation safety department. Raising awareness of the importance of dosimetry should be a priority for the occupational safety or radiation safety departments in health systems. Staff who comply with dosimeter regulations can receive feedback about where and when they are receiving radiation doses, which can help audit behaviors and promote increased safety awareness.

Other Issues

Since 1941 when I-131 was used for the treatment of thyrotoxicosis, the use of nuclear medicine for imaging and therapeutic procedures has increased at an exponential rate.[16] Nuclear medicine uses radioactive material to help diagnose and treat conditions such as cancer or cardiac disease. PET scans are an example of diagnostic imaging that involves injecting a small dosage of radiopharmaceutical material to image and measure the function of an organ. Medical administration of radiopharmaceuticals or external beam radiation therapy is used under the prescription of an authorized physician. Internal radiation therapy, or brachytherapy, is a form of nuclear medicine treatment where radiation is released from inside the body for treatment of cancer, such as non-Hodgkin lymphoma.[16] Brachytherapy comes with its side effects, which differ from ionizing radiation from medical imaging. The most common adverse reactions are thrombocytopenia, neutropenia, fatigue, nausea, vomiting, diarrhea.

Radiation exposure from various nuclear power plants has allowed us to develop basic principles of radiation protection to ensure the safety of employees and how to handle unplanned exposures. If an employee encounters a scenario where radioactive material has been spilled, it must be dealt with according to specific regulations. For example, radioactive materials should not be flushed down normal sanitation drains. They should be allowed to decay in an adequately shielded facility when they have half-lives less than 90 days.[17] Radioactive waste tags should be labeled and disposed of to radioactive waste departments. The secure storage of the waste should be maintained at all times.

Enhancing Healthcare Team Outcomes

As medical imaging evolves, so does the medical community’s understanding of how to protect people from ionizing radiation. The first step to optimizing safe radiation practice is educating hospital staff on radiation best practices. Each institution’s radiation safety department is responsible for educating and enforcing protective strategies. Protocol development and education strategies have been effective in multiple specialties. Simple interventions can play a major role in radiation dose optimization. For example, after a 20-minute video was used to educate physicians on radiation best practices, it was found to reduce median fluoroscopy time by 30% to 50%.[18] Justification, optimization, and adherence to dose limits can significantly decrease exposure when followed. Following the ALARA principle, health care workers should confirm that the benefits of the exposure outweigh the risks and strive to decrease radiation exposure as far below the dose limits as practical.