Dose-effect relationships for various responses of mammalian cells to radiations of different linear energy transfer

The following results are presented: 1) Induction of dicentrics and centric rings per cell in V-79 cells as a function of total absorbed dose, over a range 0 - 10 gy, for 300 kV x-rays, γ-rays, 0.5, 4.2, 15 MeV neutrons 2) Survival curve examples for various tumour cells and normal tissue cells, for 300 kV x-rays and 15 MeV neutrons. It was concluded that studies of dose-effect relations for various responses of mammalian cells can be used to estimate the effectiveness at small doses and low rates, which are of interest in radiation protection. The values of the parameter (a1), representing the linear component of a dose-effect relation, can be estimated if the value of the ratio of linear and quadratic components (a1/a2) is known and if actual data are available of doses, including the region where the contribution of linear and quadratic terms contribute approximately equally to the total effectiveness, and where cell killing is not yet important, i.e. less than 1 Gy. This implies that, because a1/a2 values range roughly between 0.5 and 5 Gray, data involving doses of about 0.5 to 1.0 Gy are generally sufficient to allow extrapolation to much smaller doses, without very large uncertainties. (U.K.)