Carcinogenic effects of low-level ionizing radiation: problems and prospects.

For public health purposes, the overall risks of cancer are assumed to increase in proportion to the dose of ionizing radiation, without a threshold. Assessment of the risks that may be attributable to doses below the range in which empirical data are available, however, entails the use of models, the credibility of which depends on the extent to which the models are consistent with what is known about the occurrence and mechanisms of the effects in question. Although the weight of existing evidence is consistent with the hypothesis that the risks of genetic and carcinogenic effects of ionizing radiation increase as linear-nonthreshold functions of the dose, this concept is challenged by some observers in view of growing evidence that low doses of radiation may elicit adaptive responses that enhance the repair of DNA damage and protect in other ways as well. Further research is needed to resolve the issue.