Differential Cytotoxic Effects of Hyperthermia below and above 43°C Alone or Combined with X Irradiation

Abstract

DIKOMEY, E. Differential Cytotoxic Effects of Hyperthermia below and above 430C Alone or Combined with X Irradiation. Radiat. Res. 88, 489-501 (1981). The effect of hyperthermia alone or combined with X irradiation on the proliferative capacity of CHO cells was studied for temperatures between 41 and 460C. For heat treatments in the range 41-430C or 43-460C, the Arrhenius plot yielded an inactivation energy of 417 ? 28 and 167 ? 16 kcal/mole, respectively. Hyperthermia at 42 and 450C, which by itself killed 10% of the cells, was combined with single X-ray doses ranging up to 7 Gy or with fractionated irradiation with two doses of 3 Gy. A mathematical description was developed to determine the effect of hyperthermia on repair of sublethal damage. At 370C sublethal damage was repaired with a half-time of 43.3 min. At 420C, hyperthermia accelerated the fixation of damage and enhanced repair of remaining sublethal damage, reducing the half-time to 19.3 min. In contrast, hyperthermia at 450C did not affect fixation of damage but depressed the rate of repair of sublethal damage, thus increasing the half-time to 83 min.