Lv Jianfeng, Wang Jinghui, Li Qiheng, Yang Gen, Gai Wei, Zhu Kun, Yan Xueqing
State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, People's Republic of China.
Institute of Guangdong Laser Plasma Accelerator Technology, Guangdong 510540, People's Republic of China.
Phys Med Biol. 2025 Sep 16;70(18). doi: 10.1088/1361-6560/ae0239.
The development of FLASH radiotherapy (FLASH-RT) is limited by the availability of ultra-high dose rate (UHDR) irradiation platform. This study aims to optimize electron scattering foils (SFs) for a compact 6 MeV linear accelerator (linac) operating at a short source-to-surface distance (SSD), enabling lateral uniform dose delivery with UHDR for FLASH-RT studies.Based on a custom-built linac, optimized aluminum SFs were designed using the Nelder-Mead simplex algorithm coupled with Geant4 Monte-Carlo simulations to achieve lateral dose uniformity in 10 mm of water/PMMA below the surface at a reduced SSD. Two geometric optimization strategies, namely stacked-layer structure and ring structure, were utilized for different field sizes. Dose distributions were quantified using radiochromic EBT-3 films, while the operation parameters-electron-gun anode voltage, pulse width, and pulse frequency-were modulated to explore dose rate dependencies.Utilizing an optimized stacked-layer SF and a 4 cm diameter resin collimator, uniform integrated lateral dose profiles in the first 10 mm of PMMA (flatness <5%) were measured for a 3.5 cm diameter field at 11 cm SSD. By modulating the operation parameters including anode voltage, pulse width and frequency, dose-per-pulse was continuously adjustable from 0.09 to 8.37 Gy, yielding instantaneous dose rates of 4.25 × 10to2.09×106Gy sand the mean dose rates spanning from10-2to103 Gys-1. Simulations further demonstrated that a flatness <5% was achievable for fields up to 10 cm diameter at the same SSD when using the ring structure SFs combined with large-diameter collimators.The system's capability to operate across conventional and UHDR regimes within a single framework supports comparisons of conventional radiotherapy and FLASH-RT effects with minimized systematic errors. This work offers insights into SF design methodology and facilitates incremental refinements of UHDR irradiation parameters, findings applicable to develop compact FLASH platforms based on other electron beam systems.
闪疗（FLASH-RT）的发展受到超高剂量率（UHDR）辐照平台可用性的限制。本研究旨在优化用于紧凑型6 MeV直线加速器（直线加速器）的电子散射箔（SFs），该直线加速器在短源皮距（SSD）下运行，能够在UHDR下实现横向均匀剂量输送，用于FLASH-RT研究。基于定制的直线加速器，使用Nelder-Mead单纯形算法结合Geant4蒙特卡罗模拟设计了优化的铝制SFs，以在降低的SSD下在表面以下10 mm的水/聚甲基丙烯酸甲酯中实现横向剂量均匀性。针对不同的射野尺寸，采用了两种几何优化策略，即堆叠层结构和环形结构。使用放射变色EBT-3薄膜对剂量分布进行量化，同时调节操作参数——电子枪阳极电压、脉冲宽度和脉冲频率——以探索剂量率依赖性。使用优化的堆叠层SF和4 cm直径的树脂准直器，在11 cm SSD下，针对3.5 cm直径的射野，测量了聚甲基丙烯酸甲酯前10 mm内的均匀积分横向剂量分布（平整度<5%）。通过调节包括阳极电压、脉冲宽度和频率在内的操作参数，每脉冲剂量可在0.09至8.37 Gy之间连续调节，产生的瞬时剂量率为4.25×10至2.09×106 Gy/s，平均剂量率范围为10-2至103 Gy/s。模拟进一步表明，当使用环形结构SFs与大直径准直器结合时，在相同的SSD下，对于直径达10 cm的射野，平整度<5%是可以实现的。该系统在单一框架内跨常规和UHDR模式运行的能力支持对常规放疗和FLASH-RT效果进行比较，同时将系统误差降至最低。这项工作为SF设计方法提供了见解，并有助于逐步完善UHDR辐照参数，这些发现适用于基于其他电子束系统开发紧凑型FLASH平台。
