Radiobiological Effects of Low Doses: Implications for Radiological Protection

For most biological effects that are relevant to radiobiological protection under conditions of low-level irradiation-namely, the induction of mutations, chromosome aberrations, cell killing, teratogenic effects, and the induction of neoplasms-the effectiveness per rad of low-LET radiation is reduced at low doses and low dose rates, whereas that of high-LET radiation is relatively less dose and dose rate dependent. The variations with dose, dose rate, and LET differ, however, from one type of effect to another, and in few instances have they been defined well enough to enable confident extrapolations to the exposure levels associated with occupational or natural background irradiation. Because of these radiobiological variations, and the paucity of data referable directly to human populations, it is not possible to make confident estimates of the risks associated with such low-level irradiation. At the same time, however, it is clear that risk estimates based on the linear hypothesis, involving single lin...