Department of Medical Physics, School of Physics and Technology, Wuhan University, Wuhan, China.
Cancer Radiation Therapy Center, Fifth Medical Center of Chinese PLA General Hospital, Beijing, China.
Med Phys. 2022 Aug;49(8):5387-5399. doi: 10.1002/mp.15717. Epub 2022 Jun 1.
This paper focused on the design and optimization of ridge filter-based intensity-modulated proton therapy (IMPT), and its potential applications for FLASH. Differing from the standard pencil beam scanning (PBS) mode, no energy/layer switching is required and total treatment time can be shortened.
Unique dose-influence matrices were generated as a proton beam traverses through slabs of different thicknesses (i.e., modulation by different layers). To establish the references for comparison, conventional IMPT plans (single field) were created using a large-scale nonlinear solver. The spot weights from the reference IMPT plans were used as inputs for optimizing the design of ridge filters. Two designs were evaluated: model A (static) and model B (dynamic). The ridge filter designs were first verified (by GEANT4 simulation) in a water phantom and then in an H&N case. A direct comparison was made between the GEANT4 simulation results of two models and their respective references, with regard to plan quality, dose-averaged dose rate, and total treatment time.
In both the water phantom and the H&N case, two models are able to modulate dose distributions with high conformity, showing no significant difference relative to the reference plans. Dose rate-volume histograms suggest that in order to achieve a dose rate of 40 Gy/s over 90% PTV, the beam intensity needs to be 2.5 × 10 protons/s for both models. For a fraction dose of 10 Gy, the total treatment time (including both irradiation time and dead time) can be shortened by a factor of 4.9 (model A) and 6.5 (model B), relative to the reference plans.
Two proposed designs (both static and dynamic) can be used for PBS-IMPT requiring no layer switching. They are promising candidates for FLASH-IMPT capable of reducing treatment time and achieving high dose rates while maintaining dose conformity simultaneously.
本文专注于基于脊滤波器的强度调制质子治疗（IMPT）的设计和优化，及其在 FLASH 中的潜在应用。与标准的笔束扫描（PBS）模式不同，无需进行能量/层切换，并且可以缩短总治疗时间。
独特的剂量影响矩阵是在质子束穿过不同厚度的平板时生成的（即通过不同的层进行调制）。为了建立比较的参考，使用大规模非线性求解器创建了常规的 IMPT 计划（单场）。参考 IMPT 计划中的光斑权重被用作优化脊滤波器设计的输入。评估了两种设计：模型 A（静态）和模型 B（动态）。首先在水模体中对脊滤波器设计进行验证（通过 GEANT4 模拟），然后在头颈部病例中进行验证。对两个模型的 GEANT4 模拟结果与其各自的参考进行了直接比较，比较了计划质量、剂量平均剂量率和总治疗时间。
在水模体和头颈部病例中，两种模型都能够以高适形性调节剂量分布，与参考计划相比没有显著差异。剂量率-体积直方图表明，为了在 90%PTV 上实现 40Gy/s 的剂量率，两种模型的束流强度都需要达到 2.5×10 质子/s。对于 10Gy 的分次剂量，与参考计划相比，总治疗时间（包括照射时间和死时间）可以缩短 4.9 倍（模型 A）和 6.5 倍（模型 B）。
两种提出的设计（静态和动态）都可用于无需层切换的 PBS-IMPT。它们是具有降低治疗时间和实现高剂量率的同时保持剂量适形性的 FLASH-IMPT 的有前途的候选者。
