Université de Lyon, INSA-Lyon, Université Claude Bernard Lyon 1, UJM-Saint Etienne, CNRS, Inserm, CREATIS UMR 5220, U1206, F-69008, Lyon, France. Author to whom any correspondence should be addressed.
Phys Med Biol. 2019 Mar 8;64(6):065003. doi: 10.1088/1361-6560/ab02a8.
The use of a most likely path (MLP) formalism for protons to account for the effects of multiple Coulomb scattering has improved the spatial resolution in proton computed tomography (pCT). However, this formalism assumes a homogeneous medium and a continuous scattering of protons. In this paper, we quantify the path prediction error induced by transverse heterogeneities to assess whether correcting for such errors might improve the spatial resolution of pCT. To this end, we have tracked protons trajectories using Monte Carlo simulations in several phantoms with different heterogeneities. Our results show that transverse heterogeneities induce non Gaussian spatial distributions leading to errors in the prediction of the MLP, reaching 0.4 mm in a 20 cm wide simulated heterogeneity and 0.13 mm in a realistic phantom. It was also shown that when the spatial distributions have more than one peak, a most likely path, if any, has yet to be defined. Transverse heterogeneities also affect energy profiles, which could explain some of the artifacts described in other works and could make the energy cuts usually performed to exclude nuclear events less efficient.
使用最可能路径（MLP）公式来考虑质子多次库仑散射的影响，提高了质子计算机断层扫描（pCT）的空间分辨率。然而，该公式假设介质均匀且质子连续散射。在本文中，我们量化了横向非均匀性引起的路径预测误差，以评估是否纠正这些误差可能会提高 pCT 的空间分辨率。为此，我们使用蒙特卡罗模拟在具有不同非均匀性的几个体模中跟踪质子轨迹。我们的结果表明，横向非均匀性会导致非高斯空间分布，从而导致 MLP 预测错误，在 20cm 宽的模拟非均匀性中达到 0.4mm，在现实体模中达到 0.13mm。还表明，当空间分布有多个峰时，最可能路径（如果有的话）尚未定义。横向非均匀性还会影响能量分布，这可以解释其他工作中描述的一些伪影，并且可能使通常用于排除核事件的能量切割效率降低。
