Proliferation kinetics and survival of mammal cells after treatment with radiation of various ionization densities and with hyperthermia

Survival and proliferation kinetics of chinese hamster cells after Co-γ-, π--meson irradiation, hyperthermia (40 - 430C), and a combination of Co-γ irradiation and hyperthermia were studied in this paper. After γ-irradiation, exponential-phase and stationary-phase cells showed equal survival rates for equal doses. Cytofluorometric analysis showed that there was a dose-dependent delay in the synthesis phase with subsequent cell blocking in the G2+M phase. After irradiation with π- mesons, there is a dose-dependent accumulation in the G2+M phase, with a RBE of 2.2. The different response of S-phase cells to radiations of different LET may be explained with the inactivation kinetics typical of each type of radiation. The effectiveness of hyperthermal treatment depends on the stage of growth of the cells. A temperature of 400C does not induce cell killing, not even after prolonged exposure. After 7 hours' exposure to 410C, on the other hand, 80% of the cells are killed after blocking in G2+M. Exposure to 420C for 1-2 h induces a synchronisation effect which is induced by a block in S and G2+M. After exposure to 420C for 4 h, however, the cells blocked in S are killed in this phase. Combination of Co-γ radiation leads to increased cells killing and also to sensitization, especially of cells in the exponential growth stage. The proliferation kinetics effects of this combined treatment are the same as after pion irradiation. (orig.)