Hyperthermia

In comparison with the effect of radiations, hypoxic cells were more thermolabile, and decrease in pH elevated the fatality by heat. As for the sensitivity in the cell cycle, the S phase was resistant against radiations, but sensitive against heat. Cells under growth showed low radiosensitivity in the non-proliferating phase, but showed a reverse relation by heat. Some chemical compounds with a SH group increased heat-sensitibity, as did radiations. Injury generally occurred and was completed in the same cell cycle. The interval between injury and recovery was 9 hr. for G1 phase cells and 18 hr. for S phase cells. Target agents are unknown, but protein and its analogues have been postulated. Combination with radiations brought sublethal to lethal injury of non-synchronized culture cells and showed a synergistic-totalling effect in animal studies. Radiosensitization by heat was pronounced only in tumors, and the optimal interval of treatment was 3 - 4 hr. The temperature of normal tissues stopped rising at about 430C, but the intratumoral temperature continued to rise. Tumor regression was observed in cases of marked thrombocytopenia which occurred after thermal treatment. (Chiba, N.)