Normal tissue response to fractionated heat and X-irradiation

Researchers used the mouse tail to examine normal tissue tolerance to fractionated heat and X-irradiation. Variables examined were level of heat, dose/fraction, total dose, fraction interval, and heat followed by X-irradiation versus irradiation followed by heat. With low level heat (42 degrees C, 1 hr), high total dose (6,000 rad) with high dose/fraction was needed to induce necrosis. In contrast, high heat level (44 degrees C, 30 min) induced necrosis with 1,000 rad (200 rad daily). However, the high temperature could be tolerated with a low dose/fraction and an increased interval between fractions. In general, with a higher temperature, heat before X-irradiation was more damaging than the reverse; the slopes for incidence of necrosis were steep. More work is required for the establishment of threshold doses and slopes of response for these treatment sequences