Variation in the Fatal Cancer Probability per Unit Effective Dose with Age at Exposure and Population Statistics

Abstract

Effective dose is a measure of radiation detriment, that is, the probability of an adverse consequence resulting from radiation exposure. The unit of effective dose is the sievert. Unlike the gray, a radiation dose unit with real physical meaning, the sievert includes non-dimensional factors which can vary. The sievert cannot be directly measured and the radiation detriment per sievert may not be the same in all circumstances. With the change, in ICRP 60, from 'absolute' risk to 'relative' risk, the risk that the sievert represents now depends, inter alia, on population statistics and age at exposure. With 'relative' risk, radiation exposure is assumed to have a multiplying effect on the 'natural' cancer incidence. As this varies with age and between populations, the risk per sievert will be different in different populations. Persons with unusual dose accumulation patterns or who are members of populations with vital statistics significantly different from those used by the ICRP will experience a risk per sievert different to the ICRP value. Results of calculations for populations representative of a developed country and a hypothetical developing country for a range of age at exposure are presented to illustrate the range of risks represented by the sievert. The calculations indicate that the risk per sievert is less if the dose is received later in life and is less in a developing country than in a developed country, but the range in risk is not great.