Thermal enhancement of radiation damage in previously irradiated skin.
The responses of the mouse ear to hyperthermia alone, X rays alone or X rays combined with heat were investigated at various times up to one year after prior irradiation. The initial X-ray treatments, either a single dose of 17 Gy or 34 Gy given as 10 fractions in 11 days, caused the same skin reactions (a small area of moist desquamation in a few ears) and had the same effects on the responses to subsequent treatments. The response to heat alone was increased at 3-12 months after prior irradiation, so that the heating time at 43.5 degrees C required to cause necrosis was about 70% of that in age-matched controls. The responses to X rays alone were also increased. Prior irradiation, however, had different effects on the susceptibilities to develop acute radiodermatitis and late deformity. For acute radiodermatitis, the X-ray dose required to obtain a given response in previously irradiated ears was about 90% of the dose required in age-matched controls. For deformity at 6 months, the dose was about 70%. Prior irradiation had the same effects on the responses to X rays given 6 min before mild hyperthermia (43.5 degrees C, 15 min) as on those to X rays alone. As a consequence, the thermal enhancement ratio (TER), i.e., the dose of X rays required alone to cause an effect divided by that required with heat, did not depend on previous irradiation. The TER was 1.4 for both acute radiodermatitis and late deformity.
D000818:Animals; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006358:Hot Temperature; D051379:Mice; D012867:Skin / Q000528:radiation effects*; D013997:Time Factors