[Hyperthermia and radiosensitization]

The effects of hyperthermia on tumor cells and the mechanism of radiosensitization by hyperthermia were analysed. The clinical application of hyperthermia to cancer treatment was also discussed. The heat sensitivity of cells was dependent on the exposed period and temperature. The increase in one degree Celsius of temperature enhanced twice the heat sensitivity of cells. The target of cell killing might be proteins which are associated with the membrane-energy system. The heat sensitivity was increased at low pH. A large tumor (e. g., 800 mm3 of volume) responded more to hyperthermia than a small tumor (e. g., 30 mm3). This could be explained that the large tumor contains nencosis and many low-pH cells. Repeated treatment of hyperthermia induced heat-tolerance. The same effects of hyperthermia to the tumor cells were observed on normal tissues as well. The clinical application of hyperthermia can be evaluated by the therapeutic ratio. With animal tumors, 1.5 of the therapeutic ratio was obtained. By combining hyperthermia with irradiation, the radiation effect of cell killing was enhanced. The radiosensitization increased with the temperature of hyperthermia. The mechanism of radiosensitization is due to inhibition of repair from sublethal damage and potentially lethal damage. Clinical evaluation of the combination of two modalities was done by the therapeutic gain factor. Irradiation followed by hyperthermia resulted in more than unity of the therapeutic gain factor. It might be concluded that hyperthermia can be applied to large tumor clinically, and that the treatment of hyperthermia can be applied after 2 to 4 hours of irradiation when combined.