Yagi Masashi, Furutani Keith M, Ogata Toshiyuki, Nomura Takuya, Umezawa Masumi, Liang Xiaoying, Yamada Kei, Yamazaki Hideya, Shimizu Shinichi, Beltran Chris J
Department of Carbon Ion Radiotherapy, Osaka University Graduate School of Medicine, Osaka, Japan.
Division of Medical Physics, Department of Radiation Oncology, Mayo Clinic, Jacksonville, Florida, USA.
Med Phys. 2025 Mar;52(3):1867-1877. doi: 10.1002/mp.17589. Epub 2024 Dec 16.
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.
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.
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.
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.
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.
目前所有日立质子笔形束扫描设备均采用离散点扫描（DSS）。佛罗里达州梅奥诊所（MCF）正在安装一台具备先进技术的日立粒子治疗系统，包括快速扫描速度、高束流强度、快速束流关闭控制（RBOC）、跳点功能以及使用剂量驱动连续扫描（DDCS）的质子笔形束扫描。RBOC的一个潜在问题是在正常点输送结束时，由于带有瓣剂量（FD）的瓣点（FS）会产生一个肩部，这在碳同步加速器中已被研究，但在质子输送中尚未研究。例如，虽然针对日立在MCF的安装进行了研究，但该方法可能适用于所有未来的高强度质子输送。
目前没有日立质子设备使用所提议的RBOC。本研究旨在通过在研究模式下使用日立质子机器模拟FS，了解质子FD在MCF的剂量学影响，反映MCF预期的更高质子强度下的RBOC情况。
在京都府立医科大学（KPUM）以研究模式进行实验以模拟MCF的RBOC，将延迟时间（Td）从1.5毫秒减少到0.1毫秒。在中心轴上对70.2、142.5和220.0 MeV的质子能量、正常、高剂量率（HDR）和超高剂量率（uHDR）强度以及不同Td的垂直和水平机架角度输送5000个连续点。使用快速示波器以及喷嘴的点位置监测器（SPM）和剂量监测器（DM）进行测量。开发了一个模型来预测FD对束流强度的依赖性，并评估对前列腺和脑部治疗计划的剂量学影响。计划了两种模拟类型：每个点都有FS的瓣DSS计划和仅在每层末尾有FS的瓣DDCS计划。
在Td = 0.1毫秒的RBOC中观察到了FD，显示出与机架角度无关。FD随着更高的延迟剂量率（DDR）即束流强度的增加而增加。规划研究表明，与临床计划相比，随着FD增加剂量体积直方图会恶化，但仅在uHDR强度下显著。在MCF计划的HDR强度的瓣DSS计划中恶化很小，并且瓣DDCS计划甚至比瓣DSS计划更不敏感。
MCF正在安装具有更高束流强度、跳点功能和快速束流关闭控制的质子DDCS。在预期的MCF强度下，对于DSS和DDCS的两种患者计划，产生的FD对剂量分布的影响不显著。然而，在uHDR情况下观察到了显著的依赖性。除了针对常规QA和基于日志的质子患者特定质量保证的建议外，还描述了一种在调试期间测量FS位置和剂量的方法。
