Mutation and inactivation of mammalian cells by various ionising radiations

Some studies are described on the inactivation and on the induction of mutations in cultured mammalian cells exposed to various irradiations covering a range of LETs (linear energy transfers). It was found for two cell types that the maximum mutagenic effectiveness of the radiations, relative to X or γ radiation (RBE), was about twice that for inactivation. It was also found that specific chromosome aberrations appear to be associated with mutations induced by high LET radiations. Cultures of freshly isolated human cells and of hamster cells were irradiated with He, B or N ions covering an LET range of 20 to 470 keV/μm. Dose response curves for inactivation and mutation by these radiations are shown graphically, together with plots of RBE against LET. Results are discussed and mechanisms suggested. The preliminary observations suggest that an additional mutagenic mechanism becomes important with high LET irradiations. It is considered that the data obtained provide useful empirical confirmation of current radiological protection standards. (U.K.)