Liu Paul Z Y, Dong Bing, Nguyen Doan Trang, Ge Yuanyuan, Hewson Emily A, Waddington David E J, O'Brien Ricky, Liney Gary P, Keall Paul J
ACRF Image X Institute, University of Sydney Central Clinical School, Sydney, NSW, Australia.
Department of Medical Physics, Ingham Institute for Applied Medical Research, Liverpool, NSW, Australia.
Med Phys. 2020 Dec;47(12):6440-6449. doi: 10.1002/mp.14536. Epub 2020 Nov 1.
High quality radiotherapy is challenging in cases where multiple targets with independent motion are simultaneously treated. A real-time tumor tracking system that can simultaneously account for the motion of two targets was developed and characterized.
The multitarget tracking system was implemented on a magnetic resonance imaging (MRI)-linac and utilized multi-leaf collimator (MLC) tracking to adapt the radiation beam to phantom targets reproducing motion with prostate and lung motion traces. Multitarget tracking consisted of three stages: (a) pretreatment aperture segmentation where the treatment aperture was divided into segments corresponding to each target, (b) MR imaging where the positions of the two targets were localized, and (c) MLC tracking where an updated treatment aperture was calculated. Electronic portal images (EPID) acquired during irradiation were analyzed to characterize geometric uncertainty and tracking latency.
Multitarget MLC tracking effectively accounted for the motion of both targets during treatment. The root-mean-square error between the centers of the targets and the centers of the corresponding MLC leaves were reduced from 5.5 mm without tracking to 2.7 mm with tracking for lung motion traces and reduced from 4.2 to 1.4 mm for prostate motion traces. The end-to-end latency of tracking was measured to be 328 ± 44 ms.
We have demonstrated the first experimental implementation of MLC tracking for multiple targets having independent motion. This technology takes advantage of the imaging capabilities of MRI-linacs and would allow treatment margins to be reduced in cases where multiple targets are simultaneously treated.
在同时治疗多个具有独立运动的靶区的情况下，高质量放疗具有挑战性。开发并表征了一种能够同时考虑两个靶区运动的实时肿瘤跟踪系统。
多靶区跟踪系统在磁共振成像（MRI）直线加速器上实现，并利用多叶准直器（MLC）跟踪，使辐射束适应模拟靶区，这些靶区再现前列腺和肺部运动轨迹的运动。多靶区跟踪包括三个阶段：（a）预处理孔径分割，将治疗孔径划分为与每个靶区对应的段；（b）MR成像，定位两个靶区的位置；（c）MLC跟踪，计算更新后的治疗孔径。分析照射期间采集的电子门静脉图像（EPID），以表征几何不确定性和跟踪延迟。
多靶区MLC跟踪在治疗过程中有效地考虑了两个靶区的运动。对于肺部运动轨迹，靶区中心与相应MLC叶片中心之间的均方根误差从无跟踪时的5.5毫米降至跟踪时的2.7毫米；对于前列腺运动轨迹，从4.2毫米降至1.4毫米。测量跟踪的端到端延迟为328±44毫秒。
我们展示了首个针对具有独立运动的多个靶区的MLC跟踪的实验实现。该技术利用了MRI直线加速器的成像能力，并将允许在同时治疗多个靶区的情况下减小治疗边界。
