离子成像中的单粒子跟踪不确定性
Single particle tracking uncertainties in ion imaging
摘要：
基于蒙特卡罗模拟，对单粒子离子成像跟踪系统中的路径不确定性进行了广泛的比较。空间分辨率作为系统参数的函数，如几何形状，探测器的属性和质子和氦束的能量进行了研究，作为硬件开发的指导方针。初级粒子的路径内的水体积进行采样，并比较从探测器测量获得的最有可能的路径估计，产生深度依赖的不确定性信封。将沿该曲线的最大不确定性转换为单组参数值的最小射线照相像素间距的保守估计。分析了具有各种参数设置的模拟，以获得作为系统参数的函数的可达像素间距的概述。结果用于确定探测器材料预算和位置分辨率的间隔，以产生足够小的像素间距用于临床剂量计算。为确保像素间距低于2 mm，探测器的材料预算应保持低于0.25%（位置分辨率为200 $\mathrm{μm}$）或低于0.75%（位置分辨率为10 $\mathrm{μm}$）。使用质子，对于300 mm的体模尺寸或大间隙，无法实现亚毫米像素尺寸。如果位置分辨率小于100 $\mathrm{μm}$且材料预算低于0.75%，则使用氦离子，即使对于大的体模尺寸和间隙，也可以实现亚毫米像素间距。
英文摘要：
An extensive comparison of the path uncertainty in single particle tracking systems for ion imaging was carried out based on Monte Carlo simulations. The spatial resolution as function of system parameters such as geometry, detector properties and the energy of proton and helium beams was investigated to serve as a guideline for hardware developments. Primary particle paths were sampled within a water volume and compared to the most likely path estimate obtained from detector measurements, yielding a depth-dependent uncertainty envelope. The maximum uncertainty along this curve was converted to a conservative estimate of the minimal radiographic pixel spacing for a single set of parameter values. Simulations with various parameter settings were analysed to obtain an overview of the reachable pixel spacing as function of system parameters. The results were used to determine intervals of detector material budget and position resolution that yield a pixel spacing small enough for clinical dose calculation. To ensure a pixel spacing below 2 mm, the material budget of a detector should remain below 0.25 % for a position resolution of 200 $\mathrm{μm}$ or below 0.75 % for a resolution of 10 $\mathrm{μm}$. Using protons, a sub-millimetre pixel size could not be achieved for a phantom size of 300 mm or at a large clearance. With helium ions, a sub-millimetre pixel spacing could be achieved even for a large phantom size and clearance, provided the position resolution was less than 100 $\mathrm{μm}$ and material budget was below 0.75 %.
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