Monte Carlo Simulation of High Energy Photon Imaging

描述(由申请人提供)： 这项工作的广泛长期目标是大幅改进伽马相机成像的高能单光子发射器的成像、量化和剂量测定。一个特定的长期目标是验证在两种放射性核素治疗中肿瘤消退与计算的肿瘤辐射吸收剂量之间高度显著相关的假设：1)1-131抗B1放射免疫治疗(RIT)；2)1-131间二甲基苯基胍(MIBG)治疗。在我们机构，II期1-131标记的抗B1RIT试验对滤泡性淋巴瘤的有效率为97%，完全有效率为63%。1-131RIT和MIBG治疗的成功重新引起了人们对1-131成像的兴趣，以准确地估计内部剂量。在前一阶段，对模拟I-131单光子成像的蒙特卡罗程序进行了优化和验证。模拟研究证实了目前使用单光子计算机断层扫描(SPECT)准确定量I-131活度的局限性。下一阶段的重点将是使用蒙特卡罗开发高度针对患者的方法，这些方法将显著改进肿瘤/器官剂量测定的两个主要步骤：活度量化和吸收剂量计算。针对患者的方法将通过整合SPECT和联合注册CT的信息来实施。具体地说，我们建议实现1)患者特定的部分体积校正；2)基于蒙特卡罗的前向投影器，它包括患者特定的散射；3)3)患者特定的剂量估计。此外，我们将继续评估3DOSEM重建，其中包括探测器的响应，我们将为共轭视图活动量化方法的多中心评估生成数据。这项工作将以模体研究结束，该研究建立了1-131 SPECT定量和剂量估计的最佳方法，并将这些方法应用于现有的RIT患者数据，以可能揭示剂量和肿瘤体积缩小之间的统计意义上的关系。此外，我们将尝试将来自3D剂量学的新的可用参数，如剂量不均匀和最小剂量，与肿瘤体积缩小相关联。在任何1-131RIT临床研究中都没有显示出强烈的剂量-反应关系，这可能是由于剂量估计不佳所致。在这里，我们建议结合和扩展许多工具，以显着改善估计，并朝着个性化治疗计划取得进展。

DESCRIPTION (provided by applicant): The broad long-term objective of this work is to substantially improve imaging, quantification and dosimetry of high-energy single-photon emitters imaged with gamma cameras. A specific long-term objective is to verify the hypothesis of a highly significant correlation between tumor regression and calculated tumor radiation absorbed dose in two radionuclide therapies 1) 1-131 anti-B1 radioimmunotherapy (RIT), and 2) 1-131 metaiodobenzylguanidine (MIBG) therapy. At our institution, a phase II 1-131 labeled anti-B1 RIT trial for follicular lymphoma, showed a 97% response rate and a 63% complete response rate. The success of 1-131 RIT and MIBG therapy has renewed interest in 1-131 imaging for accurate internal dose estimates. During the previous period a Monte Carlo code for modeling single-photon imaging of I-131 was optimized and validated. Simulation studies demonstrated the current limitations to accurate I-131 activity quantification using single photon computed tomography (SPECT). The focus for the next period will be on using Monte Carlo to develop highly patient-specific methods that will significantly improve the two main steps in tumor/organ dosimetry: activity quantification and absorbed dose calculation. The patient-specific methods will be implemented by integrating information from SPECT and co-registered CT. Specifically we propose to implement 1) patient-specific partial volume correction; 2) a Monte Carlo based forward projector, which includes patient-specific scatter; 3) 3-D patient-specific dose estimation. In addition, we will continue evaluation of a 3D OSEM reconstruction, which includes detector response and we will generate data for a multi-center evaluation of conjugate-view activity quantification methods. The work will culminate with phantom studies that establish the optimum methods for 1-131 SPECT quantification and dose estimation and with the application of the methods to existing RIT patient data to possibly reveal a statistically significant relationship between dose and tumor volume reduction. In addition, we will attempt to correlate newly available parameters from the 3-D dosimetry, such as dose non-uniformity and minimum dose, with tumor volume reduction. A strong dose-response relationship has not yet been demonstrated in any 1-131 RIT clinical study possibly due to poor dose estimation. Here we propose to combine and expand many tools to significantly improve the estimate and make advances towards individualized treatment planning.