Relationship between cellular radiosensitivity and non-repaired double-strand breaks studied for different growth states, dose rates and plating conditions in a normal human fibroblast line

Purpose : The aim of this study was to test under which conditions non-repaired DNA double-strand breaks (dsb) could be used as an indicator of cellular radiosensitivity of normal human fibroblasts. Materials and methods : The experiments were performed with a primary normal skin fibroblast line (NFHH) derived from a healthy donor. Cells were X-irradiated either in exponential or confluent state with high (4 Gy/min) or low dose rate (0.04Gy/min) and either plated immediately or delayed after irradiation. The fraction of clonogenic cells was determined after doses up to 12 Gy using colony forming assay and the number of non-repaired dsb were measured 24h after X-irradiation with doses up to 180 Gy using constant-field gel electrophoresis. Results : Cellular radiosensitivity of NFHH cells was found to depend on all three conditions tested. In contrast, the number of non-repaired dsb was found to depend on dose rate and growth state only. There were, however, no differences for the plating conditions tested....