Pre-treatment patient-specific stopping power by combining list-mode proton radiography and x-ray CT
Pre-treatment patient-specific stopping power by combining list-mode proton radiography and x-ray CT
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DOI：
10.1088/1361-6560/aa7c42
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发表时间：
2017-09-07
影响因子：
3.5
通讯作者：
Seco, Joao
中科院分区：
文献类型：
--
作者：
Collins-Fekete, Charles-Antoine;Brousmiche, Sebastien;Seco, Joao
相对阻止本领（RSP）的不确定性是质子治疗中射程不确定性的最大贡献者。这项工作的目的是开发一种系统的方法，通过结合（1）治疗前X射线CT和（2）患者的每日质子X线摄影，产生准确的和患者特异性的RSP。该方法被公式化为惩罚最小二乘优化问题（argmin（平行于Ax - B平行于（2）（2）。参数A表示每种材料中质子穿过的累积路径长度，通过HU上的阈值分离。材料RSP（水当量厚度/物理厚度）用x表示。参数B是使用Geant 4模拟产生的列表模式质子射线照相术。该问题使用非负线性求解器求解，其中x >= 0。通过将用三次或线性样条方法计算的质子轨迹叠加到CT来计算A。Geant 4中指定的材料RSP用于参考，而临床HU-RSP校准曲线用于比较。首先研究了Gammex RMI-467体模。估计的物料可吸入悬浮粒子与计算所得的可吸入悬浮粒子之间的标准偏差为0.45%。然后评估了技术的鲁棒性，作为投影数量和初始质子能量的函数。两个初始投影的优化产生精确的RSP（
The relative stopping power (RSP) uncertainty is the largest contributor to the range uncertainty in proton therapy. The purpose of this work was to develop a systematic method that yields accurate and patient-specific RSPs by combining (1) pre-treatment x-ray CT and (2) daily proton radiography of the patient. The method was formulated as a penalized least squares optimization problem (argmin(parallel to Ax - b parallel to(2)(2))). The parameter A represents the cumulative path-length crossed by the proton in each material, separated by thresholding on the HU. The material RSPs (water equivalent thickness/physical thickness) are denoted by x. The parameter b is the list-mode proton radiography produced using Geant4 simulations. The problem was solved using a non-negative linear-solver with x >= 0. A was computed by superposing proton trajectories calculated with a cubic or linear spline approach to the CT. The material's RSP assigned in Geant4 were used for reference while the clinical HU-RSP calibration curve was used for comparison. The Gammex RMI-467 phantom was first investigated. The standard deviation between the estimated material RSP and the calculated RSP is 0.45%. The robustness of the techniques was then assessed as a function of the number of projections and initial proton energy. Optimization with two initial projections yields precise RSP (