Experimental Measurement of Secondary Particle Count for Real-Time Proton Range Verification

The real-time positioning of the particle beam range during treatment is a critical technology for improving the quality of the patient treatment. This article presents a scheme for the real-time proton range verification, and an experimental prototype is built at the Xi’an proton application facility (XiPAF) terminal. The experiment utilized a 150 MeV passive proton beam delivery mode to bombard the polymethyl methacrylate (PMMA) target for the real-time proton range verification. This scheme utilizes the secondary particle counts generated per monitor unit (MU) of primary particles and does not require identification of the secondary particle species, only its deposition energy in the cerium bromide (CeBr3) scintillator module exceeding 73.24 keV. The accuracy of range verification was evaluated at various acquisition periods by establishing the relationship between the secondary particle counts generated per MU of primary particles and the proton range. The range verification accuracy after one spill ( $\sim ~1.67\times 10$ 9 protons) delivery was measured at $0.01~\pm ~0$ .29 mm. The accuracy of range verification within milliseconds is mainly affected by the statistical fluctuations in the secondary particle counts caused by the accumulation of activation products. Under constrained conditions, the range verification accuracy was measured at $0.16~\pm ~0$ .69 mm within 110 ms acquisition time and $0.16~\pm ~0$ .94 mm within 55 ms acquisition time. The experimental results confirm the feasibility of the scheme for the real-time range verification practice. The study hopes to provide a new reference scheme for reducing the impact of range uncertainty on the patient treatment quality.