Health Risk from Radiation Exposure

The main goal of any radiation protection program is to minimize the risk of health effects to personnel from radiation exposure. Health effects associated with exposure to ionizing radiation fall into two main categories: deterministic and stochastic. Radiation exposure regulations have been written to prevent the occurrence of deterministic effects and minimize the occurrence of stochastic effects.

Deterministic effects are those most commonly associated with extremely high, acute exposure, such as have occurred in the Japanese bomb survivors or the emergency workers at the Chernobyl accident. These effects are characterized by several factors:

• The effect is limited to the individual exposed; offspring are not affected.
• A threshold dose is required for the onset of effects. Below the threshold dose, an effect is not seen.
• The severity of the effect is directly related to the dose received.

Examples of deterministic effects are: Changes in blood cell proportions, erythema and acute radiation syndromes (GI, Hematopoietic and CNS). Deterministic effects of radiation exposure are very rare and only seen in the case of extreme accidents.

Stochastic effects are more commonly associated with chronic, low dose rate exposure, although these effects can occur subsequent to the survival of deterministic effects. Stochastic effects are characterized by the following:

• The risk of a specific health effect occurring is related to the dose received with no threshold dose required. Theoretically, some level of risk is present at any dose, no matter how low. The risk of effect increases with increasing dose.
• The severity of the effect is not related to dose. For example, an individual either has cancer, or does not; the severity of the cancer is unrelated to the dose.

The most common stochastic effect associated with exposure to ionizing radiation is cancer. The risk of death from radiation-induced cancer is thought to be in the range of 4 to 8 per 10,000 per rem. This number is controversial for a number of reasons.

• Risk estimates are based on high dose rate experiments in animals. Human exposure data is limited to accident victims. For obvious reasons, few people volunteer for this type of research.
• In medical diagnosis, it is not possible to determine if a particular cancer is caused by radiation, or some other cancer causing agent.
• In the general population, approximately 2,000 people out of 10,000 will die of cancer. The excess risk attributed to radiation exposure is difficult to calculate, since these numbers are smaller than the error associated with the total cancer mortality rate in the general population. In the comparison of actual data from occupationally exposed workers to other non-exposed populations, no difference in cancer mortality rates have been seen.

From a practical standpoint, the LLUMC Radiation Safety Program attempts to eliminate the risk of deterministic effects through procedural and engineering controls and to minimize the risk of stochastic effects through the ALARA principle.

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