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 30μm diameter and 5μm thickness was used. Simple cubic plans and patient plans using the carbon-ion beams were created by treatment planning system, and the calculated LET_dvalues were compared with the measured LET_dvalues obtained by the SOI microdosimeter.Main results.Reasonable agreement between the measured and calculated LET_dwas seen in the plateau region of depth LET_dprofile, whereas the measured LET_dwere below the calculated LET_din the peak region, specifically where LET_dexceeds 75 keVμm^-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_dvalues 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.