[Studies of the cell cycle of experimental animal tumors following X-ray treatment].

: With the aim to contribute to optimized radiotherapy the proliferation kinetic parameters in experimental animal tumors were determined. As compared to non-radiated tumors, a single X-ray dose of 3 Gy accelerated the time course of the mitotic cycle which may be interpreted as a repair response. In contrary, following a single irradiation with 12 Gy the mitotic phases were delayed in their temporal course. Surprisingly, fractionated irradiations of these tumors yielded significantly less favorable results (no tumor regression, shorter rates of survival) in comparison with those after a single high X-ray dose. Obviously, this is due to a great share of hypoxic tumor cell areas in solid Ehrlich carcinomas which cannot irreversibly be impaired by low radiation doses.