[论文解读] Intra- and Inter-Fraction Relative Range Verification in Heavy-Ion Therapy Using Filtered Interaction Vertex Imaging

Devin Hymers, Eva Kasanda+6 more|arXiv (Cornell University)|Jun 16, 2021

Radiation Therapy and Dosimetry参考文献 43被引用 4

一句话总结

该论文提出了一种过滤交互顶点成像（fIVI）方法，用于在使用16O束在聚甲基丙烯酸甲酯（PMMA）体模中相互作用产生的次级粒子时，实现重离子治疗中实时的分内和分间相对范围验证。该方法通过重建相互作用顶点并拟合其深度分布的远端边缘，检测布喇格峰位置偏移，实现了亚毫米级精度——平均值的标准偏差为220(10) μm。

ABSTRACT

Heavy-ion therapy, particularly using scanned (active) beam delivery, provides a precise and highly conformal dose distribution, with maximum dose deposition for each pencil beam at its endpoint (Bragg peak), and low entrance and exit dose. To take full advantage of this precision, robust range verification methods are required; these methods ensure that the Bragg peak is positioned correctly in the patient and the dose is delivered as prescribed. Relative range verification allows intra-fraction monitoring of Bragg peak spacing to ensure full coverage with each fraction, as well as inter-fraction monitoring to ensure all fractions are delivered consistently. To validate the proposed filtered Interaction Vertex Imaging method for relative range verification, a ${}^{16}$O beam was used to deliver 12 Bragg peak positions in a 40 mm poly-(methyl methacrylate) phantom. Secondary particles produced in the phantom were monitored using position-sensitive silicon detectors. Events recorded on these detectors, along with a measurement of the treatment beam axis, were used to reconstruct the sites of origin of these secondary particles in the phantom. The distal edge of the depth distribution of these reconstructed points was determined with logistic fits, and the translation in depth required to minimize the $\chi^2$ statistic between these fits was used to compute the range shift between any two Bragg peak positions. In all cases, the range shift was determined with sub-millimeter precision, to a standard deviation of the mean of 220(10) $\mu$m. This result validates filtered Interaction Vertex Imaging as a reliable relative range verification method, which should be capable of monitoring each energy step in each fraction of a scanned heavy-ion treatment plan.

研究动机与目标

• 开发一种非侵入性、实时的布喇格峰范围精度验证方法，用于重离子治疗期间。
• 实现对束流能量输送的分内监测，以检测由患者运动或组织不均性引起的瞬时范围误差。
• 通过比较不同治疗分次中布喇格峰深度，支持分间一致性检查。
• 通过建立稳健的相对验证框架，减少对绝对范围验证的依赖。
• 使用16O束在临床相关体模设置中验证fIVI作为临床可行技术的适用性。

提出的方法

• 使用位置敏感的硅探测器记录在40 mm PMMA体模中16O束照射期间产生的次级粒子。
• 利用探测器位置和束流轴信息，重建次级粒子的三维相互作用顶点。
• 应用过滤算法以排除背景和错误重建事件，提升顶点分辨率。
• 使用逻辑斯蒂函数拟合重建顶点深度分布的远端边缘，以确定布喇格峰深度。
• 通过最小化两个逻辑斯蒂拟合之间的χ²统计量，计算两个布喇格峰位置之间的范围偏移。
• 使用束流线数据和治疗计划坐标，追踪束流轴并确保对齐，无需实时探测器校准。

实验结果

研究问题

• RQ1 fIVI能否在重离子治疗中实现亚毫米级精度，以检测布喇格峰深度的相对偏移？
• RQ2 fIVI能否检测由患者运动或束流能量漂移引起的分内范围偏差？
• RQ3 fIVI能否可靠地比较不同治疗分次中的布喇格峰位置，以实现分间一致性？
• RQ4 fIVI在临床束流强度下，以及在离子计数减少时，性能如何变化？
• RQ5 fIVI能否在临床环境中以最小的设置和对准开销实现？

主要发现

• 在16O束实验中，fIVI对210组布喇格峰位置之间范围偏移的测量精度达到220(10) μm（1σ）。
• 该方法在PMMA体模中检测布喇格峰位置深度差异时表现出亚毫米级精度。
• 该技术成功从次级粒子中重建了相互作用顶点，分辨率足够高，可分辨微小范围偏移。
• 精度的保持无需高分辨率的单粒子追踪，从而降低了硬件要求。
• fIVI在使用相对测量方法方面，展现出实时分内监测和分间一致性检查的潜力。
• 该方法与临床实施兼容，因为探测器对准和束流轴追踪可通过计算手段实现。