Inactivation of synchronized mammalian cells with low-energy X rays--results and significance

Results for inactivation of hydroxyurea-synchronized V-79 cells by ultrasoft aluminum characteristic X rays of energy 1.5 keV are presented. Limiting RBEs at low doses, relative to 137Cs gamma rays, of 1.8 and 6.4 are, respectively, found for cells at the G1/S and late S stages of the cell cycle. The late-S data are analyzed in the light of previous experiments carried out under similar conditions, also designed to probe the effects of energy deposition in nanometer-sized sites, in which cells were irradiated with correlated pairs of ions. Within the framework of the theory of dual radiation action, the results for ultrasoft X rays and gamma rays can be deduced solely from track simulations and the results of the high-LET molecular ion experiment.