Lyon University, INSA-Lyon, University Lyon1, UJM-Saint Etienne, CNRS, Inserm, CREATIS UMR5220, U1206, France. CNRS/IN2P3 and Lyon 1 University, UMR 5822, Villeurbanne, France.
Phys Med Biol. 2018 Jul 2;63(13):135013. doi: 10.1088/1361-6560/aaca1f.
We present a comprehensive analytical comparison of four types of proton imaging set-ups and, to this end, develop a mathematical framework to calculate the width of the uncertainty envelope around the most likely proton path depending on set-up geometry, detector properties, and proton beam parameters. As a figure of merit for the spatial resolution achievable with each set-up, we use the frequency [Formula: see text] at which the modular transfer function of a density step decreases below 10%. We verify the analytical results with Monte Carlo simulations. We find that set-ups which track the angle and position of individual protons in front of and behind the phantom would yield an average spatial resolution of 0.3-0.35 lp mm assuming realistic geometric parameters (i.e. 30-40 cm distance between detector and phantom, 15-20 cm phantom thickness). For set-ups combining pencil beam scanning with either a position sensitive detector, e.g. an x-ray flat panel, or with a position insensitive detector, e.g. a range telescope, we find an average spatial resolution of about 0.1 lp mm for an 8 mm FWHM beam spot size. The pixel information improves the spatial resolution by less than 10%. In both set-up types, performance can be significantly improved by reducing the pencil beam size down to 2 mm FWHM. In this case, the achievable spatial resolution reaches about 0.25 lp mm. Our results show that imaging set-ups combining double scattering with a pixel detector can provide sufficient spatial resolution only under very stringent conditions and are not ideally suited for computed tomography applications. We further propose a region-of-interest method for set-ups with a pixel detector to filter out protons which have undergone nuclear reactions and discuss the impact of tracker detector uncertainties on the most likely path.
我们对四种类型的质子成像设备进行了全面的分析比较，并为此开发了一个数学框架，以根据设备几何形状、探测器特性和质子束参数计算最可能质子路径周围不确定性包络的宽度。作为每种设备可实现的空间分辨率的衡量标准，我们使用模块化传递函数的密度阶跃下降到 10%以下的频率[Formula: see text]。我们通过蒙特卡罗模拟验证了分析结果。我们发现，如果使用现实的几何参数（即探测器和体模之间的距离为 30-40cm，体模厚度为 15-20cm），在体模前后跟踪单个质子的角度和位置的设备将产生平均空间分辨率为 0.3-0.35 lp mm。对于将铅笔束扫描与位置敏感探测器（例如 X 射线平板）或位置不敏感探测器（例如射程望远镜）结合使用的设备，我们发现对于 8mm FWHM 束斑大小，平均空间分辨率约为 0.1 lp mm。像素信息将空间分辨率提高了不到 10%。在这两种设备类型中，通过将铅笔束尺寸减小到 2mm FWHM，可以显著提高性能。在这种情况下，可实现的空间分辨率达到约 0.25 lp mm。我们的结果表明，只有在非常严格的条件下，结合双散射和像素探测器的成像设备才能提供足够的空间分辨率，并且不适合用于计算机断层扫描应用。我们进一步提出了一种用于像素探测器设备的感兴趣区域方法，以滤除发生核反应的质子，并讨论了跟踪器探测器不确定性对最可能路径的影响。
