Feasibility of three-dimensional range verification for carbon-ion therapy by measuring secondary electron bremsstrahlung: A Monte Carlo simulation study

This study investigates the feasibility of three-dimensional secondary-electron-bremsstrahlung (SEB) imaging in carbon-ion therapy. Monte Carlo simulations were performed to model SEB generation and detection using a pinhole-based X-ray camera system. Reconstructed SEB images successfully visualized the depth and lateral distributions of carbon-ion beams under various range and lateral shift conditions. One-dimensional profile analyses using individual slices demonstrated that range and lateral shifts could be estimated with errors of up to 4.2 and 4.7 mm, respectively. When using summed profiles that integrated SEB intensity across orthogonal planes, the estimation accuracy improved, decreasing the maximum error to 1.3 mm for range shifts and 2.9 mm for lateral shifts. These results indicate that SEB-based imaging is a promising noninvasive approach for in vivo range verification and incidence localization in particle therapy. The findings provide a strong foundation for future experimental validation and system optimization toward clinical implementation of SEB imaging.