Stochastic effects of ionizing radiation occur by chance, generally occurring without a threshold level of dose. Probability of occurrence of stochastic effects is proportional to the dose but the severity of the effect is independent of the dose received. The biological effects of radiation on people can be grouped into somatic and hereditary effects. Somatic effects are those suffered by the exposed person. Hereditary effects are those suffered by the offspring of the individual exposed. Cancer risk is usually mentioned as the main stochastic effect of ionizing radiation, but also hereditary disorders are stochastic effects.
Stochastic Effects and Effective Dose
The effective dose is defined as the doubly weighted sum of absorbed dose in all the organs and tissues of the body. It is very important, whether a person is exposed partially or completelly and it is very important, whether a person is exposed to gamma rays or to another type of radiation. Effective dose allows to determine stochastic biological consequences of of all types of radiation. Dose limits are set in terms of effective dose and apply to the individual for radiological protection purposes, including the assessment of risk in general terms. Mathematically, the effective dose can be expressed as: