Simulation of physical processes with Monte Carlo methods in the keV and MeV energy range

现代医学的技术发展促进了对所涉及的物理过程的详细了解的需要。物理模型是医学物理学研究的基础，能够为放射治疗和放射学中新技术的最佳使用开发基本方法。在放射治疗中，辐射束被用来电离细胞环境并造成生物损伤以根除肿瘤。组成治疗光束的相关粒子产生局部次级粒子级联，它们在异质介质中的详细传输需要用蒙特卡罗方法模拟，以预测患者和标准环境中的能量沉积，以支持个性化放疗。在x射线计算机断层扫描（CT）中，研究患者的几何形状以诊断异常和进行治疗干预。光谱CT的新兴应用涉及光子能量在探测器水平的分辨率，这为各种先进的定量医学应用开辟了道路。为了支持这一发展，蒙特卡罗方法被广泛使用，因为它们能够模拟keV能量范围内的光子传输，包括散射的产生和辐射探测器响应的模拟，将x射线转换为电信号。蒙特卡罗模拟是必不可少的另一个具有挑战性的应用是核磁共振引导放射治疗。磁共振成像（MRI）与放射治疗直线仪的结合很有前景，可以实时地根据目标运动和其他潜在的解剖变化来给药。但是核磁共振涉及到一个外部磁场，这个磁场的强度足以扭曲放射治疗光束产生的局部粒子级联。辐射剂量分布和辐射探测器响应都要求使用蒙特卡罗方法来实现核磁共振引导放射治疗光束的精确辐射剂量测定。本研究计划的主要目的是探索蒙特卡罗粒子输运模拟在现代医学，特别是放射治疗和成像方面的各种应用。放射治疗和医学成像技术不断发展，由此产生了新的挑战，需要仔细了解控制物理过程。提出的研究计划将探索放射治疗和医学成像的实际和基础研究与蒙特卡罗粒子输运模拟。本研究的影响将有助于提高对小和动态光子束剂量学，非平衡核磁共振引导辐射剂量学的理解，以及光谱计算机断层扫描的新兴应用。

The technological developments of modern medicine foster the need for detailed understanding of the physical processes involved. Physical models are the basis of research in medical physics and enable the development of fundamental methodology for the optimal use of novel technologies in radiotherapy and radiology. In radiotherapy, radiation beams are used to ionize the cellular environment and cause biological damage to eradicate tumors. Particles of interest composing therapeutic beams produce localized cascades of secondary particles, and their detailed transport in heterogeneous media needs to be simulated with Monte Carlo methods to predict the energy deposition in patients and standard environments to support personalized radiotherapy. In X-ray computed tomography (CT), patient geometries are investigated for the diagnosis of anomalies and for therapeutic interventions. Emerging applications of spectral CT involve the resolution of photon energy at the detector level which opens the way to a variety of advanced quantitative medical applications. To support this development, Monte Carlo methods are used extensively for their ability to simulate photon transport in the keV energy range, including the production of scatter and the simulation of radiation detector response converting X-rays into electric signal. Another challenging application in which Monte Carlo simulation is essential is MRI-guided radiotherapy. The promising integration of magnetic resonance imaging (MRI) to radiotherapy linacs adapt dose delivery to the target motion and other potential anatomical changes in real time. But MRI involves an external magnetic field that is strong enough to distort localized particle cascades produced by radiotherapy beams. Both radiation dose distributions and radiation detector response require the use of Monte Carlo methods to achieve accurate radiation dosimetry of MRI-guided radiotherapy beams. The main purpose of this research program is to explore various applications of Monte Carlo particle transport simulation that are relevant to modern medicine, in particular to radiotherapy and imaging. Technologies in radiotherapy and medical imaging are continuously evolving from which arises new challenges requiring careful understanding of the governing physical processes. The proposed research program will explore both practical and fundamental research in radiotherapy and medical imaging with Monte Carlo particle transport simulation. The impact of this research will contribute towards improved understanding of small and dynamic photon beams dosimetry, non-equilibrium MRI-guided radiation dosimetry, and emerging applications of spectral computed tomography.