The cell proliferation kinetics of the tumor NK/Ly after single and fractionated irradiation by fast electrons

Using H3-thymidine, mitotic activity and DNA synthesis were studied in NK/Ly ascitic tumor cells after a single (1000 rad) and fractionated dose, the three fractionation regimes having the same total doses (1000 rad) and irradiation times (5 days) but different dose rhythms. It was shown that single irradiation depresses division of the tumor cells and DNA synthesis in them much more than a fractionated irradiation. With fractionated irradiations, an increase in the individual doses in the same time with simultaneous decrease in the number of fractionations and increase in the intervals between them resulted in an increased radiation effect. The number of pathological mitoses and degree of morphological damage were less noticeable in fractionated irradiation. Here they did not depend on the dose breakdown regime. In the post-irradiation period the number of pathological mitoses increased somewhat with time. Changes in mitotic activity and disturbance of DNA synthesis in tumor cells were not always parallel. (author)