Radiation effects: Modulating factors and risk assessment -- an overview.

Following low dose or low dose-rate exposures to ionising radiation, the principal resulting radiation-related risk is cancer. Site-specific cancer risk models have been developed that describe how the radiation-induced risk of a particular cancer type varies with the relevant tissue-specific absorbed dose of radiation. The degree of risk will also be determined by the radiation quality and the dose-rate, factors that will vary between types of radiation and cancer. Risk models also include a number of intrinsic factors that modify the radiation-related excess risk - sex, age at exposure, time since exposure, and attained age - although not all these factors enter into each site-specific model. Of some importance is how the radiation-related excess risk is transferred between populations when background incidence rates differ. For most cancer types, expert groups consider that the radiation-related excess risk in a population depends, to some extent, upon the background incidence rate, and therefore that radiation interacts with at least some of the major risk factors that determine the background risk for a person. For example, the radiation-induced risk of lung cancer depends on the degree of individual exposure to tobacco smoke, but the implicit assumption of the currently accepted risk transfer models is that interactions are a general feature of radiation-related cancer risk.