Department of Oncology, Aarhus University Hospital, Denmark.
Acta Oncol. 2011 Aug;50(6):952-9. doi: 10.3109/0284186X.2011.581693.
Target tracking is a promising method for motion compensation in radiotherapy. For image-based dynamic multileaf collimator (DMLC) tracking, latency has been shown to be the main contributor to geometrical errors in tracking of respiratory motion, specifically due to slow transfer of image data from the image acquisition system to the tracking system via image file storage on a hard disk. The purpose of the current study was to integrate direct image access with a DMLC tracking system and to quantify the tracking latency of the integrated system for both kV and MV image-based tracking.
A DMLC tracking system integrated with a linear accelerator was used for tracking of a motion phantom with an embedded tungsten marker. Real-time target localization was based on x-ray images acquired either with a portal imager or a kV imager mounted orthogonal to the treatment beam. Images were processed directly without intermediate disk access. Continuous portal images and system log files were stored during treatment delivery for detailed offline analysis of the tracking latency.
The mean tracking system latency for kV and MV image-based tracking as function of the imaging interval ΔT(image) increased linearly with ΔT(image) as 148 ms + 0.58 * ΔT(image) (kV) and 162 ms + 1.1 * ΔT(image) (MV). The latency contribution from image acquisition and image transfer for kV image-based tracking was independent on ΔT(image) at 103 ± 14 ms. For MV-based tracking, it increased with ΔT(image) as 124 ms + 0.44 * ΔT(image). For ΔT(image) = 200 ms (5 Hz imaging), the total latency was reduced from 550 ms to 264 ms for kV image-based tracking and from 500 ms to 382 ms for MV image-based tracking as compared to the previously used indirect image transfer via image file storage on a hard disk.
kV and MV image-based DMLC tracking was successfully integrated with direct image access. It resulted in substantial tracking latency reductions compared with image-based tracking without direct image access.
在放射治疗中，目标跟踪是一种很有前途的运动补偿方法。对于基于图像的动态多叶准直器（DMLC）跟踪，已经表明，由于图像数据通过硬盘上的图像文件存储从图像采集系统缓慢传输到跟踪系统，因此延迟是跟踪呼吸运动的几何误差的主要原因。本研究的目的是将直接图像访问与 DMLC 跟踪系统集成，并量化集成系统的跟踪延迟，用于基于 kV 和 MV 图像的跟踪。
使用集成直线加速器的 DMLC 跟踪系统来跟踪带有嵌入式钨标记的运动体模。实时目标定位基于与治疗束正交安装的端口成像仪或千伏成像仪获取的 X 射线图像。图像在没有中间磁盘访问的情况下直接处理。在治疗输送过程中连续存储门户图像和系统日志文件，以便对跟踪延迟进行详细的离线分析。
kV 和 MV 图像的跟踪系统延迟随着成像间隔ΔT（image）的增加而呈线性增加，kV 图像的跟踪系统延迟为 148ms+0.58ΔT（image），MV 图像的跟踪系统延迟为 162ms+1.1ΔT（image）。kV 图像基于跟踪的图像采集和图像传输的延迟贡献与 ΔT（image）无关，为 103±14ms。对于基于 MV 的跟踪，它随着 ΔT（image）的增加而增加，为 124ms+0.44*ΔT（image）。对于 ΔT（image）=200ms（5Hz 成像），与以前通过硬盘上的图像文件存储进行间接图像传输相比，kV 图像基于跟踪的总延迟从 550ms 减少到 264ms，MV 图像基于跟踪的总延迟从 500ms 减少到 382ms。
kV 和 MV 基于图像的 DMLC 跟踪已成功与直接图像访问集成。与不使用直接图像访问的基于图像的跟踪相比，它大大减少了跟踪延迟。
