Department of Medical Physics in Radiation Oncology, German Cancer Research Center, Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany.
Med Phys. 2012 Jan;39(1):109-18. doi: 10.1118/1.3665712.
The authors have developed a system that monitors intrafractional target motion perpendicular to the treatment beam with the aid of radioopaque markers by means of separating kV image and megavoltage (MV) treatment field on a single flat-panel detector.
They equipped a research Siemens Artiste linear accelerator (linac) with a 41 × 41 cm(2) a-Si flat-panel detector underneath the treatment head. The in-line geometry allows kV (imaging) and MV (treatment) beams to share closely aligned beam axes. The kV source, usually mounted directly across from the flat-panel imager, was retracted toward the gantry by 13 cm to intentionally misalign kV and MV beams, resulting in a geometric separation of MV treatment field and kV image on the detector. Two consecutive images acquired within 140 ms (the first with MV-only and the second with kV and MV signal) were subtracted to generate a kV-only image. The images were then analyzed "online" with an automated threshold-based marker detection algorithm. They employed a 3D and a 4D phantom equipped with either a single radioopaque marker or three Calypso beacons to mimic respiratory motion. Measured room positions were either cross-referenced with a phantom voltage signal (single marker) or the Calypso system. The accuracy of the back-projection (from detected marker positions into room coordinates) was verified by a simulation study.
A phantom study has demonstrated that the imaging framework is capable of automatically detecting marker positions and sending this information to the tracking tool at an update rate of 7.14 Hz. The system latency is 86.9 ± 1.0 ms for single marker detection in the absence of MV radiation. In the presence of a circular MV field of 5 cm diameter, the latency is 87.1 ± 0.9 ms. The total RMS position detection accuracy is 0.20 mm (without MV radiation) and 0.23 mm (with MV).
Based on the evaluated motion patterns and MV field size, the positional accuracy and system latency indicate that this system is suitable for real-time adaptive applications.
作者开发了一种系统，该系统借助不透射线标记物，通过在单个平板探测器上分离千伏（kV）图像和兆伏（MV）治疗野，监测与治疗束垂直的分次内靶区运动。
他们在研究型西门子 Artiste 直线加速器（linac）的治疗头下方配备了一个 41×41cm²的非晶硅平板探测器。共线几何形状允许 kV（成像）和 MV（治疗）束共享紧密对准的束轴。kV 源通常直接安装在平板成像仪的对面，向龙门架缩回 13cm，有意使 kV 和 MV 束错开，从而在探测器上实现 MV 治疗野和 kV 图像的几何分离。在 140ms 内获取两个连续的图像（第一个仅为 MV，第二个为 kV 和 MV 信号），并进行相减生成仅 kV 的图像。然后使用基于自动阈值的标记物检测算法对图像进行“在线”分析。他们使用配备单个不透射线标记物或三个 Calypso 信标的 3D 和 4D 体模来模拟呼吸运动。测量的房间位置要么与体模电压信号（单个标记物）或 Calypso 系统交叉引用。反向投影（从检测到的标记物位置到房间坐标）的准确性通过模拟研究进行了验证。
体模研究表明，成像框架能够自动检测标记物位置，并以 7.14Hz 的更新率将此信息发送到跟踪工具。在没有 MV 辐射的情况下，单个标记物检测的系统延迟为 86.9±1.0ms。在直径为 5cm 的圆形 MV 场存在的情况下，延迟为 87.1±0.9ms。总 RMS 位置检测精度为 0.20mm（无 MV 辐射）和 0.23mm（有 MV）。
根据评估的运动模式和 MV 场大小，位置精度和系统延迟表明该系统适用于实时自适应应用。
