Effect of whole body hyperthermia on radiation therapy of transplanted fibrosarcoma in Swiss mice

The exposure of normal mice to whole body hyperthermia (1 h WBH at 39 or 40 degreesC), 20 or 48 h prior to total body irradiation (TBI) with lethal do ses of gamma -rays affords significant protection as assessed by survival. The radioprotective effect of WBH, as observed in normal mice, diminished i n tumour bearing mice depending upon the size of tumour. Treatment of tumou r bearing mice with mild WBH, 20 h prior to local irrradiation (LIR), did n ot protect the transplanted tumour against radiotherapy with a single dose of 20 Gy or fractionated dose (in five fractions) of 7.5 Gy on alternate da ys. In fact, mild WBH treatment enhanced the tumour regression and increase d the mean survival time after fractionated dose therapy. However, the prio r mild WBH was found to be ineffective in protecting normal tissue, as asse ssed by skin contraction after local irradiation (50 Gy). This indicates th at mild WBH treatment given 20 h prior to local radiotherapy enhances fibro sarcoma tumour regression but cannot protect skin (normal tissue) against l ocal irradiation. It appears that radioprotection of animals by WBH may be the consequence of its radioprotective effect on haemopoietic tissues media ted through certain cytokines. Perhaps WBH may not have a radioprotective e ffect on other tissues, as evident from skin contraction studies.