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内容記述 |
Objective. Diamond and silicon detectors are increasingly popular tools for dose-averaged linear energy transfer (LET) in water Lw measurements of therapeutic ion beams. The LET measured in detector materials is linearly scaled to the LET in water using a calibration coefficient based on the mass stopping power ratio (MSPR) of water to detector material at a specific particle energy. However, because the MSPR varies with particle energy, this conventional conversion method introduces Lw errors. This study aims to quantify these errors for helium, carbon, oxygen, and neon ion beams and to propose a conversion method to reduce them.Approach. Rectangular targets were defined within a water phantom, and treatment plans were generated using helium, carbon, oxygen, and neon ion beams to achieve uniform dose distributions within the targets. The Lw distributions delivered to the water phantom by the ion beams were calculated. The dose-averaged LET distributions in water Lw,DM and Lw,Si measured by diamond and silicon detectors based on the conventional conversion method were also calculated. Furthermore, a conversion method incorporating the particle-energy dependence of the MSPR was applied to the silicon detector outputs to derive dose-averaged LET distributions Lw,Si_prop. These distributions were then compared with the corresponding Lw distributions.Main results. Given the high water equivalence of diamond, Lw,DM distributions agreed with the Lw distributions within 1% accuracy across all ion beams. In contrast, the poor water equivalence of silicon resulted in Lw,Si distributions up to 10.5% lower than the Lw distributions within the targets. However, when the energy-dependent MSPR-based conversion method was employed, the Lw, Si_prop distributions obtained with the silicon detectors showed good agreement with the Lw distributions across all ion beams.Significance. The energy-dependent MSPR-based conversion method is highly effective for silicon detectors, despite their inherently poor water-equivalence properties. Silicon detectors can be used as accurate Lw detectors in ion-beam radiotherapy. |
