HIRFL装置主动式点扫描束流配送系统的Monte Carlo模拟优化

Monte Carlo Simulation Study on Optimizing the Active Beam Delivery System at HIRFL

为获得适用于HIRFL装置主动式点扫描束流配送系统配送的碳离子束,利用Monte Carlo(MC)工具SHIELD-HIT12A研究了配送距离和微型脊形过滤器结构周期对治疗室等中心处束斑半高宽(FWHM)和剂量平坦度的影响。模拟研究发现:束流配送距离越短,束斑FWHM越小,但剂量平坦度越差;微型脊形过滤器结构周期是影响剂量平坦度的关键因素,周期越小,剂量平坦度越好。通过模拟研究得出:在HIRFL装置重离子治疗终端将真空窗设置在距等中心距离小于125 cm时,采用结构周期为2 mm微型脊形过滤器可以满足主动式点扫描照射对束斑FWHM和剂量平坦度的要求。

To obtain carbon ion beams suitable for the active spot scanning beam delivery system at the Heavy Ion Research Facility in Lanzhou （HIRFL）, the Monte Carlo program SHIELD-HIT12A was used to study the influences of beam delivery distance and structure period of mini ridge filter on full width at the half maximum （FWHM） of beam spot and dose flatness at the isocenter of the treatment room. The present simulation study shows that the shorter was the beam delivery distance, the smaller was the FWHM of beam spot, but the worse was the dose flatness. The structure period of mini ridge filter was a key factor to account for the dose flatness at the isocenter. The smaller was the structure period of mini ridge filter, the better was the dose flatness. Based on the simulation results, we conclude that 2 mm structure period for a mini ridge filter statisfies the requirements on the FWHM of beam spot and dose flatness at the isocenter for the active spot scanning beam delivery system at HIRFL when the distance between the vacuum window and the isocenter is set shorter than 125 cm in the nozzle.