Effect of microwave heating on the radiation response of the rhabdomyosarcoma.

The response of the rhabdomyosarcoma R1H of the rat was investigated after single doses of X-rays applied alone or in combination with hyperthermia. Tumours of 2.3 cm3 growing in the flank of the animals were locally irradiated with 15 and 30 Gy of 200-kV X-rays and/or heated by microwaves of 2450 MHz with a non-contact applicator. Temperature of the tumours as well as the body of the animals was measured using thermocouples. Heating the tumours at 43 degrees C for various time intervals caused a regrowth delay that increased linearly with treatment time. In combined treatments, hyperthermia was applied 20 minutes after irradiation. The rhabdomyosarcoma R1H showed an enhanced volume regression and tumour growth delay after combined treatment as compared to irradiation alone. After a single dose of 15 Gy, postirradiation treatments at 43 degrees C for 30 and 60 minutes lead to TER values of 1.3 and 1.8, respectively. After combining a dose of 30 Gy with hyperthermia at 43 degrees C (30 or 60 min), the TER values obtained ranged from 1.5 to 1.7.