CLONOGENIC CELL-SURVIVAL AND REJOINING OF DNA DOUBLE-STRAND BREAKS - COMPARISONS BETWEEN 3 CELL-LINES AFTER PHOTON OR HE ION IRRADIATION

Three cell lines, human glioma U-343MG, Chinese hamster V79-379A and h uman colon carcinoma LS-174T, were analysed for clonogenic survival an d with pulsed-field gel electrophoresis regarding induction and rejoin ing of double-strand breaks (dsb) in DNA. The cells were irradiated wi th either intermediate linear energy transfer (LET approximate to 55 k eV/mu m) He ions or with Co-60 photons and showed cell type-specific v ariations in their survival curves. The induction of dsb, per DNA unit , increased linearly with dose for both radiation qualities, and there were no cell type-dependent differences. However, the dsb induction f requency increased for all three cell lines with an RBE of 1.31+/-0.08 (SD) after He ion irradiation. All three cell lines showed biphasic d sb rejoining patterns with cell type-specific differences. The differe nces between the cell lines were somewhat smaller after irradiation wi th He ions, although the patterns were very similar to those seen afte r photon irradiation. The shoulders in the survival curves disappeared after He ion irradiations, however the cells retained the capacity to rejoin dsb. After 8-h rejoining the increase of LET to intermediate v alues did not give a higher fraction of residual dsb.