Moderate hyperthermia and low dose rate irradiation.

Moderate hyperthermia (4 h at 40 degrees C) enhances V-79 cell radiosensitivity at low irradiation dose rates with a maximum thermal enhancement ratio (TER) of 1.38. In comparison, the TER measured at acute dose rate is 1.13. Heat treatments given before and during irradiation are equally effective, and more so than postirradiation hyperthermia. Hyperthermia-induced inhibition of sublethal damage repair is a probable cause of the observed effect.