Correlation between cell killing and residual chromatin breaks measured by PCC in six human cell lines irradiated with different radiation types

Abstract

Purpose : To examine the relationship between cell killing and residual chromatin breaks after irradiation with qualitatively different types of radiation in six human cell lines. Materials and methods : Six human tumour cell lines and normal human cells were irradiated with 200kV X-rays and two carbonion beams accelerated by the Heavy Ion Medical Accelerator in Chiba (HIMAC) differing in LET. At the sample position the carbon-ion beams had LET2 values of 13.1 and 77.5 ±0.4keV/ μ m. Cell inactivation was documented by a colony assay. Residual chromatin breaks were measured by counting the number of residual chromatin fragments at 24 h, detected by the premature chromosome condensation (PCC) technique. Results : The cell lines covered a broad range of radiosensitivity. D 10 values ranged from 3.53 to 8.12 Gy for X-rays, 2.56 to 7.41 Gy for the lower LET carbon ions and 1.17 to 3.85Gy for the higher LET carbon ions. The results for residual chromatin breaks indicate that the more radiosensitive cell lines showed a greater induction of residual chromatin breaks either by X-rays or carbon-ions, and that an X-ray resistant cell line also showed resistance to carbon-ions. Cellular radiosensitivity correlated with the frequency of residual chromatin breaks. Conclusion : The detection of residual chromatin breaks by the PCC technique could be used to predict cellular radiosensitivity among qualitatively different types of radiation.