A long-term effect of X rays on thermal sensitivity of the mouse ear.

The response of the mouse ear to hyperthermia was investigated after single doses of X rays. A dose of 15 Gy, which alone caused no visible effect, increased thermal sensitivity at 1-2 weeks after irradiation. There was a slight recovery at 4-6 weeks but thermal sensitivity was still increased at 6 months. When heat treatment was given at 1 week or 24 weeks after X-ray doses ranging from 9-18 Gy, it was found that thermal sensitivity increased as the dose was increased above 10 Gy. Although there are reports which indicate that prior radiotherapy given more than two months earlier does not affect normal tissue response to the mild hyperthermia currently being used to treat patients, more aggressive heat therapy may produce unexpected responses at previously irradiated sites.