Cell population kinetics in radiation therapy: relationship of cellular surviving fraction to RBE and OER.

A two-component multitarget model of cellular radiation lethality was used to predict the effects of changing LET and oxygenation. It was assumed that with high-LET radiations there is a greater probability of direct and irreparable events and that hypoxia reduces the number of chemically-mediated indirect and reversible events. Cellular surviving fractions, relative biological effectiveness, and oxygen enhancement ratios were computed on this basis and compared with published experimental data. The model and program were then used to generate isoeffect curves for photons and neutrons, oxygenated and anoxic states, and various specific tissues and tumors.