Combined effects of radiotherapy and hyperthermia on C3H/He mouse mammary carcinoma

Response of an experimental C3H/He mouse mammary carcinoma to the combined X-ray irradiation and 2450 MHz microwave hyperthermia (43 0C, 10 min) was assayed by using delay in tumor regrowth (TRT50 assay) after the initial tumor regression. The thermal radiosensitization has been assayed in terms of TRT50 values for tumor to regrow to the same tumor size in 50 % of animals with or without hyperthermia. Enhancement ratio (E.R.) were 1.49 and 1.96 for 5 min and 10 min of heating at 43 0C immediately after irradiation respectively. No thermal damage was observed for 10 min of heating at 43 0C alone. The importance of the sequence and time interval between the two modalities was evaluated using a given constant heat treatment of 43 0C for 10 min. Hyperthermia was equally effective immediately before or after irradiation. Delayed hyperthermia after irradiation reduced the E.R. values, but some of the effect was remained apparent still at 24-48 hours. (author)