MONTE CARLO SIMULATION OF HIGH ENERGY PHOTON IMAGING

这项工作长期目标是量化高吸收率 能源放射性核素，如I-131。放射性核素I-131的定量测定 由于最近的成功，内部剂量学重新引起了人们的兴趣 放射免疫治疗在B细胞性非霍奇金淋巴瘤治疗中的应用 在密歇根大学和其他机构。这个 使用I-131标记抗B1单抗的II期RIT试验的最新数据 在这所大学，回应率为100%，71% 回复完成的百分比。我们建议使用蒙特卡罗 发展精确的I-131 SPECT定量的卡罗模拟。 一种经过验证的、快速、通用的适合于模拟的蒙特卡罗代码 高能光子发射体的SPECT成像目前还没有 可用。我们将进行广泛的验证测试，以确定 这样的代码将被应用于评估和解决有意义的 量化中的问题，如散射、穿透、衰减和 物体形状、大小和背景活动的影响。我们建议 建立在现有的SIMIND和怀疑论蒙特卡罗代码的基础上，这些代码非常好 为低能光子而建立的，最近已经 扩展到包括准直器散射和穿透，这是 对于更高能量的光子的精确建模是必不可少的。初步 SIMIND和Skeptic的I-131模拟结果的数据比较 简单几何形状的测量看起来很有希望，但它们的精度 在模拟真实的成像情况时，将通过建议的 研究。这些代码还将进行正电子SPECT(511keV)验证 光子)，作为PET的低成本替代品正受到越来越多的关注。 我们将改进和扩展这两个代码，使其包含逼真的模拟 或背向散射光子，准直器孔形状的精确建模以及 多普勒展宽等效应。两种编码中前景更好的一种 将被并行化，以实现显著的加速，这是 在模拟断层扫描采集时尤其重要。散布- 渗透校正是精确量化的先决条件， 目前工作的一个主要方面是蒙特卡罗评估 I-131SPECT的散射和准直器穿透及评价 基于光谱分析的补偿技术。满足感 拟议工作的所有目标都将能够准确地量化 它是预测治疗反应和确定治疗效果所必需的 要管理的最大活动数。除了量化，这一点 这项工作将在未来成像系统的设计中得到应用 高能光子。

The long term objective of this work is to quantify uptake of high energy radionuclides such as I-131. Quantification of I-131 for internal dosimetry has gained renewed interest due to the recent success of radioimmunotherapy (RIT) in treating B-cell non-Hodgkin's lymphoma here at the University of Michigan and at other institutions. The latest data from the phase II RIT trial using I-131 labeled anti-B1 MoAb at this university shows the response rate to be 100 percent, with 71 percent of the responses being complete. We propose the use of Monte Carlo simulation for developing accurate SPECT quantification of I-131. A verified, fast, versatile Monte Carlo code suitable for simulating SPECT imaging of higher energy photon emitters is not presently available. We will carry out extensive verification tests to establish such a code which will then be applied to assess and solve significant problems in quantification such as scatter, penetration, attenuation and effects of object shape, size and background activity. We propose to build on the existing SIMIND and SKEPTIC Monte Carlo codes that are well established for low energy photons, and which have recently been expanded to include collimator scatter and penetration which is essential for accurate modeling of higher energy photons. Preliminary data comparing I-131 simulation results of SIMIND and SKEPTIC with measurements for simple geometries appear promising but their accuracy in modeling realistic imaging situations will be tested by the proposed research. The codes will also be verified for positron SPECT (511 keV photons) which is gaining interest as a low cost alternative to PET. We will improve and expand the two codes to include realistic simulation or backscatter photons, exact modeling of collimator hole shape and effects such as Doppler broadening. The more promising of the two codes will be parallelized in order to achieve significant speed-up, which is especially important when simulating tomographic acquisitions. Scatter- penetration correction is a pre-requisite for accurate quantification, and a main aspect of the present work will be Monte Carlo evaluation of scatter and collimator penetration in I-131 SPECT and assessment of compensation techniques that are based on spectral analysis. Fulfilling all aims of the proposed work will allow for accurate quantification which is necessary to predict response to therapy and for determining maximum activity to be administered. Apart from quantification, this work will have applications in the design of future imaging systems for high energy photons.