Prediction of Cell Survival Curves from DNA Double-strand Break Repair Data for Low- and High-LET Radiation

A model developed previously (Ostashevsky 1989), was applied to calculate survival curves from the DNA double-strand break (dsb) repair data for Ehrlich ascites tumour (EAT) cells irradiated with X-rays or 3.4 MeV alpha-particles (Blöcher 1988). It is shown that the calculated curves are in agreement with experiments. The relationship between the low-dose-rate survival curve slopes for low- and high-LET radiations was obtained. Data for relatively radioresistant cells (EAT, normal fibroblasts, V-79 and CHO-K1) seem to be in agreement with the predicted numbers, while those for radiosensitive cells (AT fibroblasts and xrs-6) do not. Possible reasons for this discrepancy are discussed. In the framework of the model, three factors are important for the high RBE of alpha-particles: (1) an increased radiation yield of induced dsb; (2) a reduced dsb repair rate and (3) an increased probability of losing fragments from the DNA.