Author: Sung Woon Choi, Dong Wook Kim, Jin Sung Kim, Na Hye Kwon, Paulo Jorge Ribeiro Da Fonte 👨🔬
Affiliation: Department of Radiation Oncology, Yonsei Cancer Center, Heavy Ion Therapy Research Institute, Yonsei University College of Medicine, Coimbra Institute of Engineering, Polytechnic University of Coimbra 🌍
Purpose: In hadrontherapy, such as proton and carbon ion therapy, it is desirable, for quality assurance reasons, to have an online beam energy measurement independent from the machine parameters. Since in particle-based treatment the particles are typically sub-relativistic, the beam energy can be measured by time-of-flight measurements, involving the measurement of the time difference between the passage of the particles between two detectors at a known distance. In this communication, we propose a new algorithm for the treatment of the detector signals that has advantages over the common particle-by-particle time measurement.
Methods: Instead of particle-by-particle time measurements, very demanding on the characteristics of the detectors, we propose an algorithm based on the cross-correlation of the analog signals issuing from both detectors. This approach is investigated by a custom Monte-Carlo simulation using Matlab, encompassing different detector electrical responses, spill structures (down to continuous beam), signal-to-noise ratios, and signal sampling rates. By systematically varying these parameters, we aimed to assess the robustness and effectiveness of the cross-correlation approach under realistic conditions encountered in clinical settings.
Results: For measurement times of the order of 1-second (“pencil beam" spot), a timing precision well below 1 ps seems reachable even at a modest signal-to-noise ratio. This precision is not strongly dependent on the spill structure, although it is favorable that the beam is structured in short spills. The required data acquisition capability, 1 giga-sample per second across two channels, is within the range of modern hardware, making the method suitable for clinical implementation.
Conclusion: The proposed approach seems useful for the treatment of detector signals issuing from the time-of-flight method of energy measurement in hadrontherapy, much relaxing the requirements on the detector and offering a timing precision well below 1 ps, which would represent a timing relative accuracy below 0.1% on a 33 cm baseline.