Induction of 8-azaguanine Resistant Mutants in Human Cultured Cells Exposed to 31 MeV Protons

Summary

We report results on the induction of 8-azaguanine (8-AG)-resistant mutants in cultured human cells (EUE) exposed to 31 MeV protons. The spontaneous frequency of mutants was 5·6 ± 0·7 × 10⁻⁶ per viable cell. Gamma rays were taken as reference radiation. Expression times giving the highest frequency of mutants after 31 MeV protons and gamma irradiation were found to be about 10 days for both radiations. The dose–response relationship for mutant induction by protons, as determined at the optimal expression time, was compared to that obtained after gamma rays. The relative biological effectiveness (RBE) is 2·4 ± 0·5, this value being higher than the RBE value determined for cell survival.