Chromosome Breakage and Cell Lethality in Human Hepatoma Cells Irradiated with X rays and Carbon-ion Beams

Prediction of radiosensitivity would be valuable for heavy-ion radiotherapy. Premature chromosome condensation (PCC) technique has been a potential predictive assay in photon radiotherapy, but has not been investigated for hepatomas receiving heavy ions. Two human hepatoma cell lines, i.e., HLE and HLF, were irradiated with either 290 MeV/u carbon ions or 200 kVp X rays. Cell lethality was assayed by colony formation and compared with the unrejoined fraction of chromatin breaks as measured by PCC technique. Carbon ions at linear energy transfer (LET) of 76 keV/micron produced cell death more effectively than those of 13 keV/micron and X rays. For the cell killing, the relative biological effectiveness (RBE) of 13 and 76 keV/micron carbon ions compared with X rays was 1.10-1.24 and 2.57-2.59, respectively. Mean number of chromosomes in HLE and HLF cells was similar to each other, i.e., 60.48 and 60.28. RBEs for chromatin breaks of 13 and 76 keV/micron carbon ions were 1.30-1.31 and 2.64-2.79, respectively. A strong correlation between unrejoined chromatin breaks and cell killing for human hepatoma cells was observed irrespective of radiation quality. We conclude that PCC provides a potential predictor for the radiosensitivity of individual hepatoma that are treated with photon as well as heavy ion irradiation.