[Mathematical model of the combined effects of ionizing radiation and hyperthermia on mammalian cells].

A previously proposed mathematical model for the depiction of the effects of combined ionizing radiation and hyperthermia on yeast cells of different species was applied to the description of experimental data on mammalian cells. The model suggests that the synergistic effect of combined ionizing radiation and hyperthermia is caused by additional lethal damages arising from the interaction of "sublesions" induced by both agents. These "sublesions" are not lethal after the action of these agents, each taken alone. It has been shown that the thermal enhancement ratios are strongly determined by the ratios of radiation and hyperthermia-induced lethal damages. The model predicts that the maximal synergistic effect after a separate action of these modalities will be achieved if the former agent induces a greater part of lethal damages as compared to the latter one. It has been shown that the model depicts quantitatively the synergism of the simultaneous action of the agents used for Chinese hamster cells and predicts the maximal value of the synergistic effect, conditions under which it can be achieved and the dependence of the synergistic effect on the do se rate.