Mathematical description of synergistic interaction of hyperthermia and ionizing radiation

A simple mathematical model of simultaneous combined action of ionizing radiation and hyperthermia has been proposed. The model suggests that the synergistic interaction of ionizing radiation and hyperthermia is expected to result from the additional lethal damage arising from the interaction of sublesions induced by both agents. These sublesions are considered nonlethal after each agent taken alone. The model was applied to the quantitative analysis of the simultaneous action of hyperthermia and ionizing radiation. It predicts the dependence of synergistic interaction of the ratio of lethal events produced by every agent used, as well as the maximal value of the synergistic effect, conditions at which the maximal interactive effect can be achieved, and the dependence of synergistic effect on dose rate. The predictions of the model have been tested with four experimental data sets reported in the literature. The theory appears to be appropriate and the conclusions valid.