Chinese hamster ovary cells were irradiated with 200-kV X rays, and the total number of cells and the number of clonogenic cells were determined daily over a period of 10 days. The data may be described by the equation N = No-S. exp[a(t - 7)] + No.(l - S). exp[a{lexp(-b(t - r))}/b], where t is the time of sampling; S is the surviving fraction; a is the growth rate, which is independent of dose and amounts to 1.023 day-'; r is the division delay, which is proportional to dose (D), r = r'.D, with 7' = 0.187 day.Gy-'; and b is the rate at which the rise in the number of nonviable cells decreases with time (b is proportional to dose, b = b'.D, with b' = 0.046 day-' . Gy-'). From the equation one can determine that after a dose of 2 Gy, the number of nonclonogenic cells increases by a factor of 150 within 7 days and by a factor of 670 within 10 days. The corresponding factors after higher doses are 43 and 93 after 4 Gy, and 19 and 30 after 6 Gy, respectively. Nevertheless, the progeny of individual nonviable cells does not exceed 50 cells, indicating that a large proportion of the nonviable cells counted stems from nonproductive divisions of viable cells. Thus it is not feasible to determine the number of divisions that nonviable cells can complete after irradiation from cell count experiments.
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H. Jung (1982) studied this question.