Feasibility study of secondary-electron-bremsstrahlung imaging with a knife-edge slit camera for range verification in carbon-ion therapy

Secondary-electron-bremsstrahlung (SEB) imaging has been proposed as a method for in vivo range verification in particle therapy; however, insufficient detection sensitivity remains a major limitation, particularly under low-count conditions. In this study, we developed a knife-edge slit camera and evaluated its feasibility for carbon-ion beam range verification using one-dimensional SEB profiles. The camera consisted of a tungsten knife-edge slit collimator and a 16 × 16 Ce:GAGG scintillator array coupled to an 8 × 8 SiPM array. Experiments were performed at the Heavy Ion Medical Accelerator in Chiba using a 290 MeV/u carbon-ion beam irradiated onto a water phantom. One-dimensional SEB profiles were acquired for different beam ranges controlled by range shifters. The measured profiles shifted systematically with beam range. The profiles measured with range-shifter water-equivalent thicknesses of 0.00 and 5.27 mm were visually distinguishable. Calibration-based range estimation, evaluated by Poisson resampling of high-statistics measured profiles, yielded mean precisions of 2.76, 8.89, and 29.5 mm for 10 8 , 10 7 , and 10 6 incident carbon ions, respectively. These results demonstrate the feasibility of knife-edge slit SEB imaging for carbon-ion beam range verification and indicate that further improvement in detection sensitivity is required for measurements with smaller numbers of incident ions.