Gamma Radiation

Gamma radiation is electromagnetic radiation that has no mass and no electrical charge. Gamma radiation is emitted from the nucleus of a radioactive atom. Gamma radiation travels at the speed of light and is often referred to as a photon. Gamma rays are similar to visible light, but they have higher levels of energy. Gamma radiation is used most often in nuclear medicine procedures and in inpatient/outpatient thyroid therapy procedures.

X-rays

X-rays are very similar to gamma rays and have the same characteristics. Most x-ray photons used in medical facilities are created when electrons are accelerated to a high velocity within an x-ray tube and collide with a metal target. X-rays are predominantly used in diagnostic radiology, fluoroscopy, computed tomography (CT), and therapeutic x-ray procedures. X-rays typically provide information regarding anatomic structure.

Beta Particles

Beta particles are negatively charged particles that are emitted from an unstable nucleus. A beta particle is identical to an electron. One current medical use of beta particles involves yttrium-90, a radioactive material that emits a high-energy beta particle and is used in permanent brachytherapy procedures involving the liver.

Positrons

Positrons are positively charged beta particles emitted from the nucleus of some radionuclides. Similar to other types of radiation, positrons cause ionization as well. However, once a positron has lost most of its energy, it is annihilated when it interacts with an electron. As a result of this interaction, both particles are converted to photons. Positron-emitting radionuclides are used in positron emission tomography (PET) scans. PET scans are a newer modality that evaluates metabolic activity. PET can be used in combination with CT for more clinical information.

With each procedure using ionizing radiation there is the potential for health care worker and public exposure to radiation. Although the patient is intended to receive the radiation exposure for a medical benefit, individuals working with these patients in close proximity to the ionizing radiation sources may also be exposed to the ionizing radiation. The topics of radiation exposure and biological effects from radiation will be discussed. Methods of minimizing external exposure to radiation and preventing internal radiation exposure for the perioperative nurse will also be covered.

Deterministic Health Effects

When a tissue or an organism is exposed to very high doses of radiation (hundreds of rad) in a short period of time, the primary effect is cellular death. This is a deterministic health effect. As a result, the organ or system loses its ability to function or dies. The severity of the effect is directly related to the dose; the greater the dose, the more damage occurs. Deterministic effects exhibit a threshold radiation dose. Doses received below the threshold are not associated with adverse health effects. For example, cataract formation is evident when the lens of the eye receives a dose of approximately 200 to 300 rad (2 to 3 Gy) of gamma radiation. Note that “no radiogenic cataracts resulting from occupational exposure to x-rays have been reported. From patients who suffered irradiation of the eyes in the course of x-ray therapy and developed cataracts as a consequence, the cataractogenic threshold dose is estimated at about 200 rads” (Cember and Johnson, 2009).

Stochastic Health Effects

Stochastic health effects are health effects that occur by chance. Stochastic health effects are based on the probability of a health effect occurring and not on the severity of the effect. Regardless of a person’s exposure to ionizing radiation, there is the random chance that the individual may or may not develop cancer in his or her lifetime. The conservative assumption is, if one is exposed to radiation, there is a future, random chance of developing an adverse health effect such as cancer. Therefore the probability of a health effect occurring is proportional to the radiation dose. However, there are no early observable effects from exposure to low levels of ionizing radiation, but adverse health effects such as cancer may occur many years later. The challenge is that radiation-induced cancer is not distinguishable from cancer caused by other factors. The other factors that can contribute to a cancer are inherited traits, age, sex, physical condition, diet, cigarette smoking, and exposure to other agents.

To further understand the difference between deterministic and stochastic health effects, the terms acute dose and chronic dose will be used, respectively. With an acute dose the individual receives a radiation dose in a very short time period. If the radiation dose is large enough, adverse health effects such as reddening of the skin, loss of hair, damage to the gastrointestinal tract, and damage to the central nervous system may occur within hours or a few days after exposure. If the acute radiation levels are high enough, death may occur.

On the other hand, with chronic dose, the individual may be exposed to low levels (a few millirem [mrem] each week) of ionizing radiation over their working lifetime. These chronic doses are unlikely to cause deterministic health effects, as a result of repair of damaged cells, but may cause a delayed health effect. Exposure to large amounts of sunshine is a good analogy for explaining acute and chronic doses. If an individual were to receive an acute exposure to the sun, a severe sunburn such as skin blistering and peeling may develop. If another individual were to receive chronic, low doses of sun, it may result in a golden tan year after year. Now assume that both the sunburned individual and the tanned individual reach the age of 75 and both are diagnosed with skin cancer. The sunburned individual may develop skin cancer as a result of the one-time acute sunburn, or the sun-tanned individual may develop skin cancer as a result of the chronic, low levels of exposure to the sun over many years. Both scenarios may lead to skin cancer, and yet there are so many other factors that have not been accounted for, such as inherited traits, age, and sex, that it is almost impossible to differentiate between the skin cancers that were a result of either acute or chronic exposure to the sun.

In a medical facility the possibility of a radiation health care worker receiving a high acute dose of ionizing radiation is extremely unlikely because of the presence of a RSP involving dose monitoring, education, and dose-reduction strategies. The main concern is for those health care workers who receive chronic, low levels of radiation exposure over their working lifetime. There are many dose-response models that describe the relationship between radiation dose and health effects. For doses greater than 50 rem (500 mSv), there is a definite linear relationship between dose and additional cancer risk (NRC, 1996). Fifty rem (500 mSv) is 10 times higher than the current annual limit of 5 rem (50 mSv). Below 50 rem (500 mSv), there is no definitive relationship between dose and additional cancer risk. Because of the uncertainty in the dose-response relationship at doses below 50 rem (500 mSv), it is assumed that there is a linear zero threshold-dose response at the lower levels of radiation dose. This means that all radiation doses are assumed to have some adverse effect. This is a conservative assumption that serves as the basis for our radiation protection programs throughout the world. By incorporating the philosophy of maintaining exposures from levels of ionizing radiation as low as reasonably achievable, additional effort is made to minimize radiation doses to health care workers and members of the public.

Another category of stochastic health effects that warrants attention is the perception that radiation and birth defects are directly linked. This is often referred to as hereditary effects. If a woman is exposed to ionizing radiation and later has children, there is the misperception that the offspring will exhibit birth defects or an increased risk for cancer. This has not been observed in studies of exposed humans, and the possibility of hereditary effects exists only from studies performed on animals. For this reason, additional precautions are recommended to continuously minimize exposure to ionizing radiation. To protect against deterministic and stochastic health effects, RSPs at medical facilities incorporate procedures and policies to protect radiation workers, patients, and the public from external and internal exposure to ionizing radiation.

Finally, teratogenic effects are developmental effects caused by intrauterine exposure to ionizing radiation. Irradiation of the developing fetus is a concern because of the rapidly dividing and developing cells. The risk to the fetus is a function of gestational age at the time of radiation exposure and the radiation dose. Based on this information, the risk from ionizing radiation to the fetus and children is higher than that for adults. The data to support a teratogenic effect come from experiments using animal models and from human populations exposed to very high doses of radiation such as the atomic bomb survivors. For humans the significant teratogenic effects observed included mental retardation, intrauterine growth retardation, and cancer development such as childhood leukemia. However, not all exposures to ionizing radiation cause these effects. For most diagnostic procedures involving ionizing radiation in which the fetal dose is less than 10 rem (100 mSv), very little data exist to support teratogenic effects in humans (Duke University, 2009; Edwards, n.d.). Even though there is very little evidence of teratogenic health effects below 10 rem (100 mSv), there is enough cause for concern that RSPs have established additional policies for the declared pregnant health care worker and the pregnant patient intended to further reduce the radiation dose to the fetus. The focus of this chapter is on the health care worker, and radiation safety policies for the declared pregnant health care worker will be discussed in greater detail later in this chapter.

Maintaining Radiation Doses as Low as Reasonably Achievable

Because high doses of ionizing radiation have the potential to cause adverse health effects, the goal of a radiation protection program is to keep radiation doses below the annual limits. In addition, there is also a requirement that doses to health care workers and the general public will be maintained as low as is reasonably achievable (ALARA). RSP policies and procedures must be designed to minimize exposure to radiation as far below the limit as practical, taking into account economic and social factors. A facility cannot guarantee that its employees will receive no radiation exposure from their work with ionizing radiation, but, with implementation of policies and procedures that reduce external radiation exposure and prevent internal radiation exposure, exposure can be kept to a minimum.

Declared Pregnancy Policy

A declared pregnancy policy applies to pregnant women whose assigned duties involve exposure to ionizing radiation. Exposure to any amount of radiation is assumed to carry some amount of risk. The conservative assumption is that as the dose increases, the likelihood of biological effects from the radiation increases as well. The annual limit of radiation exposure for an occupationally exposed worker is 5 rem (50 mSv). Although this limit is designed to protect the adult radiation worker, there is also another recommended limit for the embryo/fetus of declared pregnant radiation workers. The embryo/fetus of a declared pregnant worker is limited to 0.5 rem (5 mSv) over the gestation period. A declared pregnancy policy is designed to protect the fetus of an occupationally exposed health care worker. The staff working with and around ionizing radiation have the option to declare their pregnancy in writing to their employer. This is a voluntary decision. A woman may choose to make a formal declaration at any point in her pregnancy, or she may choose not to make a formal declaration at all. In the latter case the dose to the embryo/fetus would not be evaluated or limited by the facility. However, the woman’s dose would still be subject to the limit for occupational radiation workers, typically 5 rem (50 mSv) per year.

Work restrictions for the declared pregnant health care worker are required if there is a significant potential for the embryo/fetus to receive a dose in excess of the 0.5 rem (5 mSv) limit as a result of the external exposure of its mother and/or from intakes of radioactive material by its mother. The expectation is that the radiation dose would be received at an even rate over the entire gestation period. To accurately assess the fetal dose, it is recommended that the declared pregnant health care worker receive a fetal dosimeter, which should be worn at the abdomen at about waist level (Figure 23-1). If the worker wears an x-ray–shielding apron, the fetal dosimeter must be worn under the apron. The fetal dosimeter should be exchanged monthly for analysis. A facility may elect to purchase maternity lead aprons designed specifically for use by the pregnant health care worker. Most maternity lead aprons increase lead shielding from 0.5 mm to 1.0 mm in areas to protect the fetus.

Figure 23-1 Fetal dosimeter.

(From Duke University and Duke Medicine Radiation Safety Division: Wearing your radiation dosimeter, n.d., available at: http://www.safety.duke.edu/RadSafety/​dosim/​badge_tutorial.htm. Accessed November 12, 2009.)

Related posts:

Preventing Surgical Site Infections Safety in the Perioperative Setting: Vendor Support To Count or Not to Count: A Surgical Misadventure Laser Risks and Preventive Measures for the Staff Incidence of Deep Venous Thrombosis in the Surgical Patient Population and Prophylactic Measures to Reduce Occurrence Fire Prevention in the Perioperative Setting: Perioperative Fires Can Occur Everywhere

Stay updated, free articles. Join our Telegram channel

Join