Department of Mechanical Engineering, Stanford University, Stanford, CA, USA.
Int J Radiat Oncol Biol Phys. 2012 Aug 1;83(5):1633-40. doi: 10.1016/j.ijrobp.2011.10.049. Epub 2012 Jan 26.
Emerging prolonged, hypofractionated radiotherapy regimens rely on high-dose conformality to minimize toxicity and thus can benefit from image guidance systems that continuously monitor target position during beam delivery. To address this need we previously developed, as a potential add-on device for existing linear accelerators, a novel telerobotic ultrasound system capable of real-time, soft-tissue imaging. Expanding on this capability, the aim of this work was to develop and characterize an image-based technique for real-time detection of prostate displacements.
Image processing techniques were implemented on spatially localized ultrasound images to generate two parameters representing prostate displacements in real time. In a phantom and five volunteers, soft-tissue targets were continuously imaged with a customized robotic manipulator while recording the two tissue displacement parameters (TDPs). Variations of the TDPs in the absence of tissue displacements were evaluated, as was the sensitivity of the TDPs to prostate translations and rotations. Robustness of the approach to probe force was also investigated.
With 95% confidence, the proposed method detected in vivo prostate displacements before they exceeded 2.3, 2.5, and 2.8 mm in anteroposterior, superoinferior, and mediolateral directions. Prostate pitch was detected before exceeding 4.7° at 95% confidence. Total system time lag averaged 173 ms, mostly limited by ultrasound acquisition rate. False positives (FPs) (FP) in the absence of displacements did not exceed 1.5 FP events per 10 min of continuous in vivo imaging time.
The feasibility of using telerobotic ultrasound for real-time, soft-tissue-based monitoring of target displacements was confirmed in vivo. Such monitoring has the potential to detect small clinically relevant intrafractional variations of the prostate position during beam delivery.
新兴的长时间、低分割放射治疗方案依赖于高剂量适形性，以最大限度地降低毒性，因此可以受益于在射束输送过程中持续监测靶区位置的图像引导系统。为满足这一需求，我们之前开发了一种新型的远程机器人超声系统，作为现有线性加速器的附加设备，该系统能够实时进行软组织成像。在此基础上，本研究旨在开发和描述一种基于图像的实时检测前列腺位移的技术。
在空间局部化的超声图像上实施图像处理技术，以实时生成代表前列腺位移的两个参数。在一个体模和五名志愿者中，使用定制的机器人操纵器连续对软组织靶区进行成像，同时记录两个组织位移参数（TDP）。评估了在没有组织位移的情况下 TDP 的变化，以及 TDP 对前列腺平移和旋转的敏感性。还研究了该方法对探头力的稳健性。
以 95%的置信度，该方法在体内前列腺位移超过 2.3、2.5 和 2.8mm 之前检测到了前-后、上-下和左-右方向的位移。在 95%的置信度下，前列腺俯仰角在超过 4.7°之前被检测到。总系统时间滞后平均为 173ms，主要受超声采集率限制。在没有位移的情况下，假阳性（FP）不超过每 10 分钟连续体内成像时间 1.5 个 FP 事件。
使用远程机器人超声进行实时、基于软组织的靶区位移监测的可行性在体内得到了证实。这种监测有可能在射束输送过程中检测到前列腺位置的小的临床相关的分次内变化。
