Formula to estimate the thermal enhancement ratio of a single simultaneous hyperthermia and radiation treatment.

An experimental model composed of a C3H mammary carcinoma and its surrounding skin has been exposed to simultaneous radiation and hyperthermia given with different combinations of heating time and temperature. Based on the thermal enhancement ratio (TER) values obtained in the temperature range 41.5 to 43.5 degrees C, a linear relationship between TER and the heating time was achieved at each temperature. The slopes of the curves drawn at each temperature were found to have a log-linear relationship with the treatment temperature. With these relationships it was possible to make a formula expressing the TER as a function of treatment temperature and time. This formula gives a crude but probably acceptable estimate of the TER following a single simultaneous radiation and heat treatment. Although subject to several limitations, the formula represents an attempt to describe a heat dose concept for the radiosensitizing effect of hyperthermia. This may be useful to establish the tolerance level of a given radiation treatment when combined with hyperthermia.