Fractionation studies with combined X rays and hyperthermia in vivo

The combined effects of single and fractionated doses of X rays and local heat were investigated using an experimental fibrosarcoma and normal mouse skin. Thermal enhancement ratios were measured from pairs of dose-response curves for both tumour and skin, and the therapeutic advantage of each treatment was then assessed by comparing the enhancement for tumour and skin. For single doses there was a therapeutic advantage when heat was applied three hours after X rays but not with heat applied immediately after irradiation. For two and five daily fractions with heat immediately after irradiation there was significantly less thermal sensitization in tumour than in skin; hence there was a therapeutic loss. When heat was applied at three hours after each fraction there was no thermal sensitization in either skin or tumour; the therapeutic ratio was therefore 1.0. The repair capacity of skin after fractionated X rays alone, or in combination with heat, was also investigated. Heat immediately after X rays caused a small decrease in the repair capacity between two fractions but no decreased repair capacity was observed with five fractions.