REPAIR OF RADIATION-INDUCED DNA DOUBLE-STRAND BREAKS IN HUMAN FIBROBLASTS IS CONSISTENT WITH A CONTINUOUS-SPECTRUM OF REPAIR PROBABILITY

Purpose: To propose a novel interpretation of DNA double-strand break (dsb) repair based an the distribution of energy micro-deposition. Mat erials and methods: Double-strand break repair curves were studied eit her after irradiation at 4 degrees C or at 37 degrees C (low dose rate ). Two human fibroblast cell lines were used: a control line, HF19, an d an ataxia telangiectasia repair-deficient line, AT5BI. Irradiations were made with gamma-rays or alpha-particles (Am-241). Repair data wer e fined by the variable repair half-time (VRHT) model. Assuming that e ach dsb has its own inherent repair half-time (IRHT) and that the VRHT is the average of the IRHT at any time during repair, the distributio n of the IRHT was calculated. Results: At the end of the irradiation, the distribution was a continuous asymmetric curve with a maximum of d sb having a short IRHT. After 1 h of repair, the curve became bell-sha ped. There is a striking similarity between the distribution of dsb re pair half-times and that of energy micro-deposition described by Goodh ead et al. (1993). Conclusion: This similarity suggests a possible cau sal relationship between the energy density deposition and the repair rate or the probability of dsb repair.