MONTE CARLO SIMULATION OF HIGH ENERGY PHOTON IMAGING

这项工作的长期目标是量化高 放射性核素如I-131。 I-131的定量 由于最近的成功， 放射免疫疗法（RIT）治疗B细胞非霍奇金淋巴瘤 在密歇根大学和其他机构。 的 使用I-131标记的抗B1单克隆抗体的II期RIT试验的最新数据 在这所大学，回复率为100%， 百分之一的答案是完整的。 我们建议使用Monte Carlo模拟用于开发I-131的精确SPECT定量。 一个经过验证的，快速的，多功能的蒙特卡罗代码，适用于模拟 目前还没有更高能量光子发射器的SPECT成像。 available. 我们将进行广泛的验证测试， 这样一个守则，然后将适用于评估和解决重大 量化方面的问题，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SKEPTIC蒙特卡罗代码， 为低能量光子建立的，最近已经被 扩展到包括准直器散射和穿透， 这对于更高能量光子的精确建模至关重要。初步 数据比较I-131模拟结果的SIMIND和SKEPTIC与 简单几何形状的测量似乎很有希望，但它们的精度 在模拟逼真的成像情况下，将测试所提出的 research. 还将验证正电子SPECT（511 keV）的代码 光子），其作为PET的低成本替代物而受到关注。 我们将改进和扩展这两个代码，以包括逼真的模拟 或反向散射光子，准直器孔形状的精确建模， 如多普勒展宽效应。 两种代码中更有希望的一种 将被并行化，以实现显著的速度提升， 在模拟断层摄影采集时尤其重要。分散- 穿透校正是精确量化的先决条件， 目前工作的一个主要方面将是蒙特卡罗评估 I-131 SPECT中的散射和准直器穿透以及 基于光谱分析的补偿技术。履行 拟议工作的所有目标都将允许准确量化 这对于预测治疗反应和确定 最大限度地发挥管理作用。 除了量化之外， 这项工作将应用于未来成像系统的设计， 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.