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

Abstract

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 290MeV/u carbon ions or 200kVp 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 76keV/μ m produced cell death more effectively than those of 13keV/μ m and X rays. For the cell killing, the relative biological effectiveness (RBE) of 13 and 76 keV/μ m 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 76keV/μ m 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.