Verification of linear energy transfer optimized carbon-ion radiotherapy.

Objective. Linear energy transfer (LET) verification was conducted using a silicon-on-insulator (SOI) microdosimeter during the commissioning of LET-optimized carbon-ion radiotherapy (CIRT). This advanced treatment technique is expected to improve local control rates, especially in hypoxic tumors. Approach. An SOI microdosimeter with a cylindrical sensitive volume of 30 μ m diameter and 5 μ m thickness was used. Simple cubic plans and patient plans using the carbon-ion beams were created by treatment planning system, and the calculated LET _d values were compared with the measured LET _d values obtained by the SOI microdosimeter. Main results. Reasonable agreement between the measured and calculated LET _d was seen in the plateau region of depth LET _d profile, whereas the measured LET _d were below the calculated LET _d in the peak region, specifically where LET _d exceeds 75 keV μ m ^-1 . The discrepancy in the peak region may arise from the uncertainties in the calibration process of the SOI microdosimeter. Excluding the peak region, the average ratio and standard deviation between measured and calculated LET _d values were 0.996 and 7%, respectively. Significance. This verification results in the initiation of clinical trials for LET-optimized CIRT at QST Hospital, National Institutes for Quantum Science and Technology.
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