Effect of dose rate on cell killing and DNA strand break repair in CHO cells exposed to internal β-rays from incorporated [3H]thymidine

Survival as well as repair of DNA strand breaks were studied in CHO cells after exposure to internal β-rays from incorporated [3H]thymidine at 40C (equivalent to an exposure at 'infinitely high' dose rate) and at 370C (low dose rate). DNA strand breaks were determined by the alkaline unwinding technique. In cells exposed at 40C cell killing was five times higher (Dsub(o) = 250 decays per cell) than in cells exposed at 370C (Dsub(o) = 1280 decays per cell). Strand breaks induced by 3H decay at 370C were repaired with the same kinetics as those generated at 40C. Therefore the different degrees of cell killing at 40C and 370C cannot be attributed to a difference in the repair kinetics for DNA strand breaks. (author)