Zafar Ahmal Jawad, Yang Xiaofeng, Diamond Zachary, Sibo Tian, Yu David, Patel Pretesh R, Zhou Jun
Department of Radiation Oncology and Winship Cancer Institute, Emory University, Atlanta, Georgia, USA.
Med Phys. 2025 Sep;52(9):e18109. doi: 10.1002/mp.18109.
In our previous study, we developed a modular pin ridge filter (pRF) design framework to streamline assembly, enabling the fast manufacture of custom filters optimized for single-energy proton FLASH planning.
In this paper, we propose a method to optimize adaptive proton FLASH therapy (ADP-FLASH) using modularized pRFs by recycling module pins from the initial plan while reducing pRF adjustments in adaptive FLASH planning.
Initially, single energy (250 MeV) FLASH-pRF plans were created using pencil beam directions (PBDs) from initial IMPT plans on the planning CT (pCT). PBDs are classified as new/changed (ΔE > 5 MeV) or unchanged by comparing spot maps for targets between pCT and re-CT. We used an iterative least-square regression model to identify recyclable PBDs with minimal relative changes to spot MU weighting. Two PBDs with the least square error were retrieved per iteration and added to the background plan, and the remaining PBDs were reoptimized for the adaptive plan in subsequent iterations. The method was validated on three liver SBRT cases (50 Gy in five fractions) by comparing various dosimetric parameters across initial pRF plans on pCT, re-CT, and the ADP-FLASH-pRF plans on re-CT.
V for initial-pRF plans on pCT, re-CT, and ADP-FLASH-pRF plans for the three cases were as follows: (93.7%, 89.2%, 91.4%), (93.5%, 60.2%, 91.7%), and (97.3%, 69.9%, 98.8%). We observe a decline in plan quality when applying the initial pRF to the re-CT, whereas the ADP-FLASH-pRF approach restores quality comparable to the initial pRF on the pCT. FLASH effect of the initial pRF and ADP pRF plans were evaluated with a dose and dose rate threshold of 1 and 40 Gy/s, respectively, using the FLASH effectiveness model. The proposed method recycled 91.2%, 71%, and 64.7% of PBDs from initial pRF plans for the three cases while maintaining all clinical goals and preserving FLASH effects.
This study validated a method for recycling the pRFs in single-energy proton FLASH planning for SBRT cases. This framework offers a scalable solution for adaptive proton therapy, balancing clinical effectiveness and practicality.
在我们之前的研究中，我们开发了一种模块化针状脊滤波器（pRF）设计框架，以简化组装过程，从而能够快速制造针对单能质子FLASH计划进行优化的定制滤波器。
在本文中，我们提出了一种方法，通过在自适应FLASH计划中回收初始计划中的模块针脚并减少pRF调整，使用模块化pRF优化自适应质子FLASH治疗（ADP-FLASH）。
最初，使用来自计划CT（pCT）上初始调强质子治疗（IMPT）计划的笔形束方向（PBD）创建单能（250 MeV）FLASH-pRF计划。通过比较pCT和重复CT上靶区的点图，将PBD分类为新的/变化的（ΔE>5 MeV）或未变化的。我们使用迭代最小二乘回归模型来识别斑点MU权重相对变化最小的可回收PBD。每次迭代检索两个误差最小的PBD并添加到背景计划中，其余PBD在后续迭代中针对自适应计划重新优化。通过比较pCT上的初始pRF计划、重复CT上的初始pRF计划以及重复CT上的ADP-FLASH-pRF计划的各种剂量学参数，在三个肝脏立体定向放射治疗（SBRT）病例（5次分割，50 Gy）上验证了该方法。
三个病例在pCT上的初始pRF计划、重复CT上的初始pRF计划以及ADP-FLASH-pRF计划的V值如下：（93.7%，89.2%，91.4%）、（93.5%，60.2%，91.7%）和（97.3%，69.9%，98.8%）。当将初始pRF应用于重复CT时，我们观察到计划质量下降，而ADP-FLASH-pRF方法恢复了与pCT上初始pRF相当的质量。使用FLASH有效性模型，分别以1 Gy和40 Gy/s的剂量和剂量率阈值评估初始pRF和ADP pRF计划的FLASH效应。所提出的方法在保持所有临床目标并保留FLASH效应的同时，从三个病例的初始pRF计划中回收了91.2%、71%和64.7%的PBD。
本研究验证了一种在SBRT病例的单能质子FLASH计划中回收pRF的方法。该框架为自适应质子治疗提供了一种可扩展的解决方案，平衡了临床有效性和实用性。
