Effect of multiple-dose irradiation on repair capacity in plateau phase C3H 10T1/2 cells

Using plateau phase C3H 10T1/2 cells, we studied the effect of multiple-dose irradiation on the repair capacity of cells after further irradiation. Cells were irradiated with repeated doses of 2.5 Gy delivered two fractions per day at 6 to 7 hours interval. The cell survival after exposure to 1 to 9 fractions was lower above 5 fractions as compared to that predicted by calculating from single dose survival curve by assuming that cells retain their capacity to repair radiation damage after each fraction. Repair kinetics experiments showed that cells were less able to repair potentially lethal damage after test dose following multiple dose irradiations. There was, however, no difference in the ability to repair sublethal damage and potentially lethal damage sensitive to anisotonic treatment in preirradiated and untreated cells. Thus, it would appear that an enhancement of the lethal expression of potentially lethal damage of three types of damage may, at least in part, contribute to the difference between the cell survival curve after multiple fractions and that predicted by calculation.