Evaluation of diamond and silicon detectors for linear energy transfer measurements of therapeutic helium, carbon, oxygen, and neon ion beams

Abstract Objective. Diamond and silicon detectors are increasingly popular tools for dose-averaged linear energy transfer (LET) in water L ¯ w 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 L ¯ w 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 L ¯ w distributions delivered to the water phantom by the ion beams were calculated. The dose-averaged LET distributions in water L ¯ w, DM and L ¯ w, 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 L ¯ w, Si _ prop. These distributions were then compared with the corresponding L ¯ w distributions. Main results. Given the high water equivalence of diamond, L ¯ w, DM