Department of Medical Physics, University of Wisconsin, Madison, WI 53705, USA.
Med Phys. 2012 Apr;39(4):2163-9. doi: 10.1118/1.3697529.
In external-beam radiation therapy, existing on-board x-ray imaging chains orthogonal to the delivery beam cannot recover 3D target trajectories from a single view in real-time. This limits their utility for real-time motion management concurrent with beam delivery. To address this limitation, the authors propose a novel concept for on-board imaging based on the inverse-geometry Scanning-Beam Digital X-ray (SBDX) system and evaluate its feasibility for single-view 3D intradelivery fiducial tracking.
A chest phantom comprising a posterior wall, a central lung volume, and an anterior wall was constructed. Two fiducials were placed along the mediastinal ridge between the lung cavities: a 1.5 mm diameter steel sphere superiorly and a gold cylinder (2.6 mm length × 0.9 mm diameter) inferiorly. The phantom was placed on a linear motion stage that moved sinusoidally. Fiducial motion was along the source-detector (z) axis of the SBDX system with ±10 mm amplitude and a programmed period of either 3.5 s or 5 s. The SBDX system was operated at 15 frames per second, 100 kVp, providing good apparent conspicuity of the fiducials. With the stage moving, detector data were acquired and subsequently reconstructed into 15 planes with a 12 mm plane-to-plane spacing using digital tomosynthesis. A tracking algorithm was applied to the image planes for each temporal frame to determine the position of each fiducial in (x,y,z)-space versus time. A 3D time-sinusoidal motion model was fit to the measured 3D coordinates and root mean square (RMS) deviations about the fitted trajectory were calculated.
Tracked motion was sinusoidal and primarily along the source-detector (z) axis. The RMS deviation of the tracked z-coordinate ranged from 0.53 to 0.71 mm. The motion amplitude derived from the model fit agreed with the programmed amplitude to within 0.28 mm for the steel sphere and within -0.77 mm for the gold seed. The model fit periods agreed with the programmed periods to within 7%.
Three dimensional fiducial tracking with approximately 1 mm or better accuracy and precision appears to be feasible with SBDX, supporting its use to guide radiotherapy.
在外部射束放射治疗中，与射束传输方向正交的现有机载 X 射线成像链无法实时从单个视图中恢复 3D 靶轨迹。这限制了它们在与射束传输同时进行实时运动管理方面的应用。为了解决这一限制，作者提出了一种基于逆几何扫描束数字 X 射线（SBDX）系统的新型机载成像概念，并评估了其在单次视图内递送基准跟踪中的可行性。
构建了一个包含后壁、中央肺体积和前壁的胸部体模。两个基准分别放置在肺腔之间的纵隔嵴上：一个 1.5 毫米直径的钢球在上部，一个金圆柱体（2.6 毫米长×0.9 毫米直径）在下部。体模放置在一个正弦运动的线性运动台上。基准运动沿 SBDX 系统的源-探测器（z）轴进行，幅度为±10 毫米，编程周期为 3.5 秒或 5 秒。SBDX 系统以每秒 15 帧的速度、100 kVp 运行，为基准提供了良好的显影度。在运动台上，探测器数据被采集，并随后使用数字断层合成技术重建为 15 个平面，每个平面之间的平面间隔为 12 毫米。在每个时间帧的图像平面上应用跟踪算法，以确定每个基准在（x，y，z）空间相对于时间的位置。对测量的 3D 坐标拟合 3D 时间正弦运动模型，并计算拟合轨迹的均方根（RMS）偏差。
跟踪运动是正弦的，主要沿源-探测器（z）轴进行。跟踪的 z 坐标的 RMS 偏差范围为 0.53 至 0.71 毫米。从模型拟合得出的运动幅度与编程幅度相差 0.28 毫米，与钢球一致，与金种子相差-0.77 毫米。模型拟合周期与编程周期相差在 7%以内。
SBDX 似乎可以实现具有约 1 毫米或更好精度和准确度的 3D 基准跟踪，支持其用于指导放射治疗。
