The effect of preirradiated tumour bed on the response of a murine fibrosarcoma to elevated temperatures.

The effect of pretransplantation irradiation of tumour beds (tumour bed effect or TBE) on the response of tumours to elevated temperatures and on the kinetics of thermo-tolerance was studied. Animal tumours were early generation isotransplants of a fibro-sarcoma, FSa-II in C3Hf/Sed mice. The tumour bed or murine foot was irradiated with 0.8 or 16 Gy in air, and tumour cell suspensions were transplanted 1-35 days thereafter. Hyperthermia of various durations was given in a 45.5 degrees C water bath when tumours reached an average diameter of 6 mm (110 mm3), and the tumour growth (TG) time to reach 500 mm3 was obtained. Dose-response curves between the TG time and the treatment time were less steep for tumours in preirradiated tumour beds than for tumours in non-irradiated tumour beds, indicating that the tumours in preirradiated tumour beds were more resistant to hyperthermia compared to the tumours in normal tumour beds. This resistance appeared to increase with increasing preirradiation dose. Thermotolerance was equally developed in tumours in normal and preirradiated tumour beds. The time required to develop the maximum thermotolerance was identical for both tumours. This indicated that the TBE has no effect on the kinetics of thermotolerance. The implication of these results in clinical trials may be that the tumour which recurred after radiotherapy may not be a good candidate for hyperthermia.