Development and Performance Evaluation of a Prompt Gamma Imaging System for Real-time Proton Therapy Monitoring

The advantage of proton therapy over conventional photon therapy is compromised by proton range uncertainty and dose monitoring is of critical importance to improve the precision of proton therapy. In this work, we report the design and performance evaluation of a prompt gamma imaging (PGI) system being developed in our lab, with high spatial resolution, high sensitivity and 2D imaging capability for real-time proton therapy monitoring. Key components of the PGI system include a multi-slit tungsten collimator, a scintillation detector array based on BGO block and SiPM, a customized ASIC-based readout electronics and a White Rabbit (WR) switch-based data acquisition electronics. Initial experimental evaluation of the detector module with the system electronics demonstrated the feasibility of the detector module for prompt gamma detection. Spatial resolution, sensitivity and Bragg peak positioning accuracy of the system was investigated with GATE simulations. The sensitivity measured at FOV center was 0.251%. ~2 mm spatial resolution was achieved for different FOV regions in both X and Y directions with slightly better spatial resolution in X direction. Bragg peak positioning accuracy was quantified by positioning bias and root mean square error (RMSE) of the most distal edge position (MDEP) of the reconstructed prompt gamma images and evaluated under different count levels. With the count level increasing from 10 ⁴ to 10 ⁶ , a sharp decrease in MDEP error from 2.29 mm to 0.76 mm was observed, indicating improved Bragg peak positioning accuracy under higher count levels and excellent Bragg peak positioning capability of the PGI system. To conclude, the designed PGI system is viable for proton therapy monitoring. Further system assembling and experimental performance evaluation in real proton therapy facility are ongoing.