Design optimization of scanning magnets for the carbon-ion radiotherapy

Subjects: Physics >> Nuclear Physics Subjects: Physics >> Interdisciplinary Physics and Related Areas of Science and Technology submitted time 2024-08-09

Ben Fan Bin Tang Pai Xiang Geng Wei Yuan Chen Xian-Hu Zeng Rong Zhou Rui-Cheng Yan Yue-Hu Pu

Abstract： Scanning magnets are devices responsible for deflecting particles to specific locations in particle therapy utilizing spot scanning techniques. To ensure the distortion of the scanned beams’ shapes remains within an acceptable level, it is necessary to guarantee that the homogeneity of the field integrals is sufficiently high in the two transversal directions within the good field region. Typically, this is accomplished by adding shims on both sides of magnet poles. In this study, we innovatively proposed a method to perform multi-objective optimization of shim parameters and excitation currents by the state-of-the-art evolutionary algorithm Non- dominated Sorting Genetic Algorithm-III (NSGA-III). Furthermore computer vision (CV) was implemented to automatically evaluate both the beam shape distortions and the centroids of the scanned beam spots at the target plane to assist efficient optimization process. With this method, optimal parameters of scanning magnets which have capability of scanning a carbon beam of 400 MeV/u beam energy across a 20 cm × 20 cm field size with a source-to-axis distance of 255 cm were obtained successfully. Meanwhile, we also conducted eddy current and temperature rise analysis, laminated steel plates with 19 slits cut near the pole gaps were used to reduce eddy
currents due to rapid variation of magnetic fields during the scanning process. Based on the optimized magnets
parameters, eddy current and temperature analyses were performed and the temperature rises were found to be near 40°C and 54°C for the Y and X magnets respectively at the designed scanning speeds, which meets the requirements for normal operation. This proposed procedure of optimization is expected to facilitate efficient and sophisticated design of various magnets applied to charged particle accelerators.

Peer Review Status:Awaiting Review

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