Effects of Hyperthermia at 50℃ on V-79 Cells in vitro

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V-79 cells were X-irradiated and/or heated at 42℃, 44℃ and 50℃ in water bath and colonized in vitro. To and Tq at 50℃ were estimated as about 0.1 minute and theoretically less than 1.0 minute respectively. Arrhenius like plot did'nt bend at any temperatures between 43℃ and 50℃, as reported elsewhere1). Preheated cells at 42℃ for 2 hours were resistant to the successive heating at 50℃, while those at 50℃ for 80 seconds were sensitized to that at 42℃. The survival fraction ratio, i. e. products of survival fractions from independent treatment with 4.5 Gy and with 50℃, respectively, divided by a survival fraction from a combined treatment with 4.5 Gy and 50℃, showed that the longer 50℃ heating period gave the more synergistic damage. Postirradiation heating periods were conditioned to give the equal survivals from single heat treatment at 42℃, 44℃ and 50℃ for the estimation of thermal enhancement ratio in Do, i. e. 1.98, 1.98 and 1.64 respectively. Heating at 50℃ showed the given cell killing rate for the shortest period among the temperatures assayed but did'nt seem essentially to give the more thermal radio-enhancement ratio by itself.