A differential effect of prior heat treatment on the thermal enhancement of radiation damage in the ear of the mouse.

The effect of prior heat treatment on thermal enhancement of radiodermatitis was investigated in the ear of the mouse. Ears were heated by immersion in hot water. A priming treatment of 43.5°C for 30 min (H) was given at various times before a second combined treatment of hyperthermia at 43.5°C (h) given immediately before (hX) or after (Xh) a dose of X rays (X). The effect of H was measured in two ways: (1) The heating time ${\rm h}_{{\rm r}}$ required to cause a given enhancement of radiodermatitis was estimated by fixing X and varying the duration of h. (2) The thermal enhancement ratio, defined as the dose of X rays alone divided by the dose of X rays with heat required to cause a given reaction, was measured by fixing h and varying X. The priming treatment H reduced the skin response to hX. This effect was such that at 24 to 96 hr after H, the heating time ${\rm h}_{{\rm r}}$ had to be increased to about 1.5 times that required without prior hyperthermia. In ...