The response of mouse skin to combined hyperthermia and X-rays.

The effects of combined hyperthermia and X-irradiation were studied in the skin of the mouse ear. Ears were heated for 1 hour by immersion in a waterbath at temperatures ranging from 37 degrees C--43 degrees C. These heat treatments had little visible effect alone, but when combined with X-rays, enhanced the radiation response. Enhancement depended on the degree of heating. When heat was given immediately after X-rays, the radiation dose to cause a given skin reaction had to be reduced by about 10 per cent for 37 degrees C and about 40 per cent of 43 degrees C. The timing and sequence of the two treatments were important. Heat after X-rays was less effective than heat before X-rays. When heat followed X-rays, the enhancing effect was lost completely if the interval exceeded 4 hours. When heat preceded X-rays, the effect was lost more slowly, depending on temperature. The implications of this for the treatment of cancer by combined therapy are discussed.