Brigham and Women's Hospital, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA, USA.
Phys Med Biol. 2013 Jun 21;58(12):4195-204. doi: 10.1088/0031-9155/58/12/4195. Epub 2013 May 28.
Compensation of target motion during the delivery of radiotherapy has the potential to improve treatment accuracy, dose conformity and sparing of healthy tissue. We implement an online image guided therapy system based on soft tissue localization (STiL) of the target from electronic portal images and treatment aperture adaptation with a dynamic multi-leaf collimator (DMLC). The treatment aperture is moved synchronously and in real time with the tumor during the entire breathing cycle. The system is implemented and tested on a Varian TX clinical linear accelerator featuring an AS-1000 electronic portal imaging device (EPID) acquiring images at a frame rate of 12.86 Hz throughout the treatment. A position update cycle for the treatment aperture consists of four steps: in the first step at time t = t0 a frame is grabbed, in the second step the frame is processed with the STiL algorithm to get the tumor position at t = t0, in a third step the tumor position at t = ti + δt is predicted to overcome system latencies and in the fourth step, the DMLC control software calculates the required leaf motions and applies them at time t = ti + δt. The prediction model is trained before the start of the treatment with data representing the tumor motion. We analyze the system latency with a dynamic chest phantom (4D motion phantom, Washington University). We estimate the average planar position deviation between target and treatment aperture in a clinical setting by driving the phantom with several lung tumor trajectories (recorded from fiducial tracking during radiotherapy delivery to the lung). DMLC tracking for lung stereotactic body radiation therapy without fiducial markers was successfully demonstrated. The inherent system latency is found to be δt = (230 ± 11) ms for a MV portal image acquisition frame rate of 12.86 Hz. The root mean square deviation between tumor and aperture position is smaller than 1 mm. We demonstrate the feasibility of real-time markerless DMLC tracking with a standard LINAC-mounted (EPID).
在放射治疗中补偿目标运动有提高治疗准确性、剂量一致性和保护健康组织的潜力。我们基于电子射野影像中的目标软组织定位（STiL）和使用动态多叶准直器（DMLC）的治疗孔径自适应，实现了一种在线图像引导治疗系统。在整个呼吸周期中，治疗孔径与肿瘤同步实时移动。该系统在配备 AS-1000 电子射野影像装置（EPID）的瓦里安 TX 临床直线加速器上实现和测试，该 EPID 以 12.86 Hz 的帧率在整个治疗过程中获取图像。治疗孔径的位置更新周期由四个步骤组成：在 t = t0 时的第一步抓取一帧，在第二步使用 STiL 算法处理该帧以获得 t = t0 时的肿瘤位置，在第三步预测 t = ti + δt 时的肿瘤位置以克服系统延迟，在第四步，DMLC 控制软件计算所需的叶片运动并在 t = ti + δt 时应用它们。在治疗开始之前，使用代表肿瘤运动的数据对预测模型进行训练。我们使用动态胸部体模（4D 运动体模，华盛顿大学）分析系统延迟。我们通过使用几个肺肿瘤轨迹（从肺放疗期间的基准跟踪记录）驱动体模，在临床环境中估计目标和治疗孔径之间的平均平面位置偏差。成功证明了无基准标记的肺部立体定向体部放射治疗的 DMLC 跟踪。对于 12.86 Hz 的 MV 射野影像采集帧率，发现固有系统延迟为 δt = (230 ± 11) ms。肿瘤和孔径位置之间的均方根偏差小于 1mm。我们使用标准 LINAC 安装的（EPID）证明了无标记 DMLC 实时跟踪的可行性。
