[Comparison of tumor cell behavior following single daily or multiple daily (accelerated) irradiation in mammary cancer in C3H mice].

The comparison of two fractionation schemes, i.e. the usual irradiation once a day with 2 Gy (SDF) and the fractionation with 3 times 1.6 Gy per day (MDF) at intervals of at least four hours shows the stronger action of higher fractionation on the destruction of tumor cells and the inhibition of their proliferation cinetics. So the number of pycnotic cells is considerably increased in case of multiple daily irradiation, and the mitosis rate as well as the labelling index show a more significant decrease. In case of one irradiation per day, the number of pycnotic cells increases during radiotherapy, too, but the mitosis rate and the labelling index only decrease until the fifth or sixth treatment day, remaining then unchanged or increasing slightly. This suggests a recurring multiplication of tumor cells already during radiotherapy. The higher efficacy of multiple daily fractionation in rapidly proliferating tumors is proved by the measurements of changing tumor volumes in the living animal during irradiation as well as by the observation of the survival time after irradiation.