Dosimetric study of synchrotron rapid beam off control and skip spot function for high beam intensity proton therapy

IF 3.2 2区医学 Q1 RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING

Medical physics Pub Date : 2024-12-16 DOI:10.1002/mp.17589

Masashi Yagi, Keith M. Furutani, Toshiyuki Ogata, Takuya Nomura, Masumi Umezawa, Xiaoying Liang, Kei Yamada, Hideya Yamazaki, Shinichi Shimizu, Chris J. Beltran

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Abstract

Background

All Hitachi proton pencil beam scanning facilities currently use discrete spot scanning (DSS). Mayo Clinic Florida (MCF) is installing a Hitachi particle therapy system with advanced technologies, including fast scan speeds, high beam intensity, rapid beam off control (RBOC), a skip spot function, and proton pencil beam scanning using dose driven continuous scanning (DDCS). A potential concern of RBOC is the generation of a shoulder at the end of the normal spot delivery due to a flap spot (FS) with a flap dose (FD), which has been investigated for carbon synchrotron but not for proton delivery. While investigated, for instance, for Hitachi's installation at MCF, this methodology could be applicable for all future high intensity proton deliveries.

Purpose

No Hitachi proton facility currently uses the proposed RBOC. This study aimed to understand the dosimetric impact of proton FD at MCF by simulating the FS with a Hitachi proton machine in research mode, reflecting the higher proton intensities expected with RBOC at MCF.

Method

Experiments were conducted to simulate MCF RBOC at Kyoto Prefecture University of Medicine (KPUM) in research mode, reducing delay time (Td) from 1.5 ms to 0.1 ms. 5,000 contiguous spots were delivered on the central axis for proton energies of 70.2, 142.5, and 220.0 MeV; at normal, high dose rate (HDR), and ultra-high dose rate (uHDR) intensities; and at vertical and horizontal gantry angles for different Td. Measurements were taken using a fast oscilloscope and the nozzle's spot position monitor (SPM) and dose monitor (DM). A model was developed to predict FD dependence on beam intensity and assess the dosimetric impact for prostate and brain treatment plans. Two simulation types were planned: a flap DSS plan with FS at every spot and a flap DDCS plan with FS only at the end of each layer.

Result

FD was observed for RBOC with Td = 0.1 ms, showing no gantry angle dependence. FD increased with higher delayed dose rate (DDR), that is, beam intensity. The planning study showed dose volume histogram deterioration with increased FD compared to the clinical plan, but it was only significant for uHDR intensities. Deterioration was marginal in flap DSS plans for the HDR intensities planned at MCF, and flap DDCS plans were even less sensitive than flap DSS plans.

Conclusion

MCF is installing proton DDCS with higher beam intensities, a skip spot function, and fast beam-off control. The resulting FD had an insignificant impact on dose distribution for two patient plans with both DSS and DDCS at the anticipated MCF intensities. However, significant dependence was observed in the case of uHDR. A method to measure the position and dose of the FS during commissioning is described in addition to recommendations for regular QA and log-based proton patient-specific quality assurance.

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高束强质子治疗中同步加速器快束失控和跳点函数的剂量学研究。

背景：目前，所有日立质子铅笔束扫描设备都使用离散点扫描（DSS）。佛罗里达梅奥诊所（MCF）正在安装一套日立粒子治疗系统，该系统采用了先进的技术，包括快速扫描速度、高束流强度、快速束流关闭控制（RBOC）、跳斑功能以及使用剂量驱动连续扫描（DDCS）的质子铅笔束扫描。RBOC 的一个潜在问题是，在正常光斑传输的末端会产生一个肩，这是由于具有瓣剂量（FD）的瓣光斑（FS）造成的。虽然这种方法是针对日立公司在 MCF 的装置进行研究的，但可适用于所有未来的高强度质子输送。本研究旨在通过模拟日立质子机在研究模式下的 FS，了解质子 FD 对 MCF 的剂量学影响，以反映 MCF 的 RBOC 预计会产生的更高质子强度：在京都府立医科大学（KPUM）以研究模式进行了模拟 MCF RBOC 的实验，将延迟时间（Td）从 1.5 毫秒缩短到 0.1 毫秒。在质子能量为 70.2、142.5 和 220.0 MeV 时，在正常、高剂量率（HDR）和超高剂量率（uHDR）强度下，以及在不同 Td 的垂直和水平龙门角度下，在中心轴上投放了 5,000 个连续光点。测量使用了快速示波器、喷嘴的光斑位置监测器（SPM）和剂量监测器（DM）。开发了一个模型来预测 FD 与射束强度的关系，并评估前列腺和脑部治疗计划的剂量学影响。我们计划了两种模拟类型：在每个光点都有 FS 的瓣膜 DSS 计划和仅在每个层末端有 FS 的瓣膜 DDCS 计划：结果：在 Td = 0.1 毫秒的 RBOC 中观察到了 FD，与龙门角度无关。延迟剂量率（DDR）（即光束强度）越高，FD 越大。与临床计划相比，计划研究显示，随着延迟剂量率的增加，剂量体积直方图会恶化，但这只对超高剂量率强度有显著影响。对于 MCF 计划的 HDR 射束强度，瓣区 DSS 计划的恶化程度微乎其微，而瓣区 DDCS 计划的敏感性甚至低于瓣区 DSS 计划：结论：MCF 正在安装具有更高射束强度、跳斑功能和快速关束控制的质子 DDCS。由此产生的 FD 对在 MCF 预期强度下同时使用 DSS 和 DDCS 的两个患者计划的剂量分布影响不大。然而，在 uHDR 的情况下，观察到了明显的依赖性。除了定期质量保证和基于日志的质子患者特定质量保证的建议之外，还介绍了一种在调试期间测量 FS 位置和剂量的方法。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Medical physics 医学-核医学

CiteScore

6.80

自引率

15.80%

发文量

660

审稿时长

1.7 months

期刊介绍： Medical Physics publishes original, high impact physics, imaging science, and engineering research that advances patient diagnosis and therapy through contributions in 1) Basic science developments with high potential for clinical translation 2) Clinical applications of cutting edge engineering and physics innovations 3) Broadly applicable and innovative clinical physics developments Medical Physics is a journal of global scope and reach. By publishing in Medical Physics your research will reach an international, multidisciplinary audience including practicing medical physicists as well as physics- and engineering based translational scientists. We work closely with authors of promising articles to improve their quality.