Long-term thermal sensitivity of previously irradiated skin.

The response of the mouse ear to hyperthermia was investigated at 7-64 weeks after irradiation with X rays. Thermal sensitivity was increased by 12 weeks after single doses of 18 to 20 Gy but showed no further changes up to 64 weeks after exposure. It is suggested that the increase in sensitivity to retreatment by hyperthermia several months after the initial course of radiation may be related to the turnover time of the tissue. Although there are reports which suggest that prior irradiation, given more than two months earlier, does not affect the response of human skin or superficial tumours to the mild hyperthermic treatment in current clinical use, more aggressive heat therapy may produce unexpectedly severe responses in previously irradiated sites.