Residual γH2AX after irradiation of human lymphocytes and monocytes in vitro and its relation to late effects after prostate brachytherapy

Background and purposeRetention of γH2AX foci in irradiated cells can signify a deficiency in DNA double-strand break repair that may be useful as an indicator of individual radiosensitivity.Materials and MethodsTo examine this possibility, the retention of γH2AX after irradiation was compared using white blood cells from 20 prostate brachytherapy patients who developed late normal tissue toxicity and 20 patients with minimal toxicity. Peripheral blood lymphocytes and monocytes were coded for analysis, exposed in vitro to 4 doses of 0.7 Gy X-rays at 3 hourly intervals, and retention of γH2AX was measured by flow cytometry 18 hours after the final irradiation.ResultsExcellent reproducibility in duplicate samples and a range in residual γH2AX from 7% above background to 244% above background were observed. Residual γH2AX in lymphocytes showed a positive correlation with patient age. However, no relation was observed between the level of residual γH2AX in peripheral blood mononuclear cells and late normal tissue damage.ConclusionsWe conclude that the method of detection of residual γH2AX after in vitro irradiation of lymphocytes and monocytes was simple, reproducible, and sensitive. However, it failed to predict for late normal tissue toxicity after brachytherapy. Possible reasons are discussed.