The relationship between the time of fractionated and single doses of radiation and hyperthermia on the sensitization of an in vivo mouse tumor

The present study was undertaken to explore the relationship of the time interval between application of heat and irradiation on enhanced tumor cell sensitivity. Using the Ridgway osteogenic sarcoma grown in AKD₂F_t/J mice, local tumor hyperthermia (42.5±.5°C for 15 minutes) was applied at various time intervals before or after single or fractionated doses of x irradiation. Enhancement of tumor cell sensitivity by combined treatment with radiation and heat, as measured by delay in tumor growth, cure rates, and mean survival times was inversely proportional to the time interval between application of both modalities. The interactions associated with this increased sensitivity appear to be transitory, diminishing with time between treatments. Possible mechanisms of action for thermal sensitization may involve the reduction of oxygen dependence as well as a reduced recovery capacity of tumor cells.