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 pr edictive assay in photon radiotherapy, but has not been investigated for he patomas 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. C ell lethality was assayed by colony formation and compared with the unrejoi ned fraction of chromatin breaks as measured by PCC technique. Carbon ions at linear energy transfer (LET) of 76 keV/mu m produced cell death more eff ectively than those of 13 keV/mu m and X rays. For the cell killing, the re lative biological effectiveness (RBE) of 13 and 76 keV/mu m carbon ions com pared 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 an d 60.28. RBEs for chromatin breaks of 13 and 76 keV/mu m carbon ions were 1 .30-1.31 and 2.64-2.79, respectively. A strong correlation between unrejoin ed chromatin breaks and cell killing for human hepatoma cells was observed irrespective of radiation quality. We conclude that PCC provides a potentia l predictor for the radiosensitivity of individual hepatoma that are treate d with photon as well as heavy ion irradiation.