Importance of Thermotolerance for Radiothermotherapy as Assessed Using Two Human Melanoma Cell Lines

Abstract

In the combined treatment of tumors by means of hyperthermia and ionizing radiation, the sequence, the interval between the two treatments, and the frequency of heat treatments are still open questions. In this discussion the development of thermotolerance plays an important role. It has frequently been observed that cells become more thermoresistant during prolonged heating at relatively low temperatures or during fractionated application of hyperthermia (review see: Henle and Dethlefsen 1978; Dewey et al. 1971; van Beuningen and Streffer 1985; Field and Law 1978; Law 1979; Law et al. 1979; Palzer and Heidelberg 1979; Law 1981; Field and Anderson 1982). The phenomenon of thermotolerance could be very important for the clinical use of hyperthermia if it also occurred in connection with radiosensitization by hyperthermia in human tumors. Up to now most studies on thermotolerance have been performed with hyperthermia alone and only a few experiments have been done with the combination of ionizing radiation and hyperthermia (Henle et al. 1979; Freeman et al. 1979; Law 1979; Nielsen and Overgaard 1979; Stewart and Denekamp 1980; van Beuningen et al. 1982; Nielsen 1984; Holohan 1982; Dewey 1984; Havemann 1983a; Streffer and van Beuningen 1983; Jorritsma et al. 1984; van Rijn et al. 1984; Jung et al. 1986; Streffer et al. 1984). The results are conflicting. Furthermore, it is very difficult to prove the existence of thermotolerance in vivo. The aim of the presented studies is to show how radiation can interact with heat treatments, especially after fractionated modalities.