Effect of hyperthermia on the radiation response of Chinese hamster small intestine

Chinese hamster small intestine was surgically exteriorised from the ligament of Trietz to the ileocaecal junction and heated for 8 min at 44.30 (a non-lethal dose) at various intervals before or after whole-body 60Co irradiation. Hyperthermia exposure immediately after irradiation reduced the LDsub(50/7) from the control of 1,230 cGy to 798 cGy (thermal enhancement ratio, TER, of 1.5). At an interval between irradiation and hyperthermia of 2 h, the LDsub(50/7) was 935 cGy for intervals of 2-24 h. The increase in the LDsub(50/7) by 2 hours after irradiation probably represents the repair of radiation damage that can interact with hyperthermia and after two hours the two modalities interact independently. When the small intestine was exposed to 44.30 hyperthermia immediately prior to irradiation, the LDsub(50/7) was reduced to 658 cGy (TER = 1.8). As hyperthermia and radiation treatments were separated, LDsub(50/7) returned to the control value by 24 h and was unchanged over 24-72 h. For the sequence hyperthermia → radiation, 33% of the hyperthermia damage was repaired by 1 h; for radiation → hyperthermia, 85% of the radiation damage was repaired by 1 h. (U.K.)