Interpretation of the dose and LET dependence of RBE values for lethal lesions in yeast cells.

Survival data on yeast cells proficient or deficient in the repair of DNA double-strand breaks (dsb) and data on the induction of dsb are used to interpret the dose dependence of the RBE value for lethal lesions after irradiation at high dose rate followed by 72-hr liquid holding providing optimum conditions for repair of potentially lethal lesions (RBEDP, DP = delayed plating). The radiations applied are conventional (150 kV), soft (50 kV), and ultrasoft (4 kV) X rays, 30-MeV electrons (or 60Co gamma rays), and 3.5-MeV alpha particles. Analysis shows that the dose dependence of the RBEDP value can be explained by the combination of two dose-independent RBE values, one for the single-particle traversal effect (RBEspt) and the other for the accumulation of dsb (RBEdsb) due to the traversal of more than one particle through the cell nucleus. Furthermore, it is shown that the LET dependence of RBEspt values describing the linear component of the lethal lesions must be considered separately for "electron" and "particle" radiations.