Cheng Xinyi, Yang Dongxu, Zhong Yuncheng, Shao Yiping
Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX 75057, United States of America.
Phys Med Biol. 2022 May 26;67(11). doi: 10.1088/1361-6560/ac6d9f.
Although positron emission tomography (PET) can provide a functional image of static tumors for RT guidance, it's conventionally very challenging for PET to track a moving tumor in real-time with a multiple frame/s sampling rate. In this study, we developed a novel method to enable PET based three-dimension (3D) real-time marker-less tumor tracking (RMTT) and demonstrated its feasibility with a simulation study.For each line-of-response (LOR) acquired, its positron-electron annihilation position is calculated based on the time difference between the two gamma interactions detected by the TOF PET detectors. The accumulation of these annihilation positions from data acquired within a single sampling frame forms a coarsely measured 3D distribution of positron-emitter radiotracer uptakes of the lung tumor and other organs and tissues (background). With clinically relevant tumor size and sufficient differential radiotracer uptake concentrations between the tumor and background, the high-uptake tumor can be differentiated from the surrounding low-uptake background in the measured distribution of radiotracer uptakes. With a volume-of-interest (VOI) that closely encloses the tumor, the count-weighted centroid of the annihilation positions within the VOI can be calculated as the tumor position. All these data processes can be conducted online. The feasibility of the new method was investigated with a simulated cardiac-torso digital phantom and stationary dual-panel TOF PET detectors to track a 28 mm diameter lung tumor with a 4:1 tumor-to-backgroundFDG activity concentration ratio.The initial study shows TOF PET based RMTT can achieve <2.0 mm tumor tracking accuracy with 5 frame ssampling rate under the simulated conditions. In comparison, using reconstructed PET images to track a similar size tumor would require >30 s acquisition time to achieve the same tracking accuracy.With the demonstrated feasibility, the new method may enable TOF PET based RMTT for practical RT applications.
尽管正电子发射断层扫描（PET）可以为放射治疗（RT）引导提供静态肿瘤的功能图像，但传统上PET要以每秒多帧的采样率实时跟踪移动肿瘤极具挑战性。在本研究中，我们开发了一种新方法，以实现基于PET的三维（3D）实时无标记肿瘤跟踪（RMTT），并通过模拟研究证明了其可行性。对于获取的每条响应线（LOR），基于TOF PET探测器检测到的两个伽马相互作用之间的时间差，计算其正电子 - 电子湮灭位置。在单个采样帧内采集的数据中，这些湮灭位置的累积形成了肺肿瘤以及其他器官和组织（背景）中正电子发射体放射性示踪剂摄取的粗略测量3D分布。鉴于临床相关的肿瘤大小以及肿瘤与背景之间足够的放射性示踪剂摄取浓度差异，在测量的放射性示踪剂摄取分布中，高摄取的肿瘤可以与周围低摄取的背景区分开来。使用紧密包围肿瘤的感兴趣体积（VOI），VOI内湮灭位置的计数加权质心可以计算为肿瘤位置。所有这些数据处理都可以在线进行。使用模拟的心脏 - 躯干数字体模和固定的双面板TOF PET探测器，研究了该新方法的可行性，以跟踪直径为28 mm、肿瘤与背景FDG活性浓度比为4:1的肺肿瘤。初步研究表明，在模拟条件下，基于TOF PET的RMTT在5帧/秒的采样率下可实现<2.0 mm的肿瘤跟踪精度。相比之下，使用重建的PET图像跟踪类似大小的肿瘤需要>30秒的采集时间才能达到相同的跟踪精度。鉴于已证明的可行性，该新方法可能使基于TOF PET的RMTT用于实际的RT应用。
