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内容記述 |
1．Purpose： Carbon-ion radiotherapy for stage-I non-small cell lung cancer (NSCLC) has been conducted at QST with 18-, 9-, 4-, and single-fraction schedules. The prescribed dose level was optimized for each fractionation schedule through dose escalation clinical studies. The purpose of this study was to investigate the effects of the radiobiological 5Rs, radiosensitivity, repopulation, repair, redistribution, and reoxygenation, on the 3-year tumor control probability (TCP) of patients with stage I NSCLC treated with carbon-ion radiotherapy.2．Methods： A meta-analysis of published clinical data of 233 NSCLC patients treated by carbon-ion radiotherapy under 18-, 9-, 4-, and single-fraction schedules was conducted. The microdosimetric kinetic model (MKM)-based cell-survival model incorporating the radiobiological 5Rs was developed to reproduce the clinical TCP data. Redistribution and reoxygenation were regarded together as a single phenomenon and termed “resensitization” in the model. The optimum interval between fractions was investigated for each fraction schedule using the determined model parameters.3．Result： The clinical TCP data for 18-, 9-, and 4-fraction schedules were reasonably reproduced by the model without the resensitization effect, whereas its incorporation was essential to reproduce the TCP data for all fraction schedules including the single fraction. The curative dose for the single-fraction schedule was estimated to be 49.0 Gy, which corresponds to the clinically adopted dose prescription of 50.0 Gy. For multi-fraction schedules, a 2-to-3-day interval is required to maximize the resensitization effect during the interval. In contrast, in the single-fraction schedule, the shorter treatment time is preferable to reduce the effect of sub-lethal damage repair during the treatment.4．Conclusion： The effects of the radiobiological 5Rs on the 3-year TCP of patients with stage-I NSCLC treated with carbon-ion radiotherapy were investigated. All 5Rs including the resensitization effect affect the clinical effectiveness of carbon-ion radiotherapy. |
