[In-vivo-examinations of the relative radiosensitivity of hypoxic tumor cells (author's transl)].

The rate of cellular losses of hypoxic respectively euoxic cells of the solid experimental tumor "sarcoma 180" was examined in vivo after irradiations with gamma rays, 15 MeV neutrons, and alpha particles. The tumor cells were labeled in vivo, at first with 125I-UdR and after 50 hours with 131I-UdR. After a further interval of about 20 hours the tumor was irradiated. This method of double labeling makes it possible to determine externally the rates of cellular losses in the labeled zones of tumor cells presenting different partial oxygen pressures. The increase of the rates of cellular losses among the euoxic and hypoxic tumor cells induced by the gamma radiation differs by 2.6; it decreases, however, to 1.5 after injection of nitrofurazone prior to the irradiation. After irradiation with 15 MeV neutrons, a difference of only 1.4 was observed. If the tumors were irradiated internally with alpha particles from the reaction 10B(n,alpha) 7Li, there was no difference between the two rates of cellular losses. As far as the above mentioned kinds of radiation are concerned, the ratios from the increase of the rates of cellular losses induced by radiation are well corresponding to the oxygen enhancement found by other authors during their examinations in vitro.