SENSITIZATION OF LOW-DOSE-RATE IRRADIATION BY NONLETHAL HYPERTHERMIA

To assess whether hyperthermia could radiosensitize cells irradiated at a low dose rate, Chinese hamster V79 cells were simultaneously heated and irradiated at 0.86 Gy/h. The data showed that heat treatments at 39 and 40°C, which did not induce heat killing alone or high-dose-rate radiosensitization, resulted in enhanced cell killing with low-dose-rate irradiation. The dose-modification factor (ratio of the slopes of the curves for low dose rate and high dose rate) was reduced to 1.8 at 39°C and 1.4 at 40°C, compared to a value of 2.1 at 37°C. These data indicate that nonlethal heat treatments can cause enhanced radiosensitization under low-dose-rate conditions. The implications of these results for interstitial thermoradiotherapy are discussed.