Revaluation for problem of clinical particle therapy in cell biological effects of proton, carbon-ion and X-ray at Hyogo Ion Beam Medical Center

Hyogo Ion Beam Medical Center (HIBMC) is the world’s only facility to provide both proton and carbon-ion radiotherapy. Based on the characteristic, HIBMC conduct and investigate many comparative studies between proton radiotherapy and carbon-ion radiotherapy. In several comparative studies, we have the problem whether there are differences between proton and carbon-ion radiotherapy. We aimed to compare and clear cell biological effects in related to good clinical results in synchrotron-proton and carbon-ion beam, using radiological, cell biological and molecular biological approach. We mainly examined effects using human salivary gland cancer (HSG cells). Cells were irradiated from 2 to 6 points in each experiment along a 150 MeV, a 320 MeV carbon- ion and a linac 4MV X-ray. We examined cell viability and relative biological effectiveness (RBE) by colony formation assay and CCK-8 colorimetric assay. A linac 4MV X-ray was used as a reference. RBE values calculated from cell survival curve for proton in HSG cells at the dose that would reduce cell survival to 10% (D10) were 1.10 by colony formation assay and 1.29 by CCK-8 colorimetric assay. RBE values at a D10 for carbon-ion in HSG cells were 1.96 by colony formation assay and 1.90 by CCK-8 colorimetric assay. These results suggest that proton beam have greater deficiency on CCK-8 colorimetric reaction than cell growth process. We thought the problem in clinical particle therapy could be partly explained by the difference in the deficiency. Furthere, we examined DNA breaks by expression in phosphorylated protein of histone H2AX and generation of Reactive oxygen Species. We reported the effective results of synchrotron-proton and carbon-ion.