Padilla Laura, Pearson Erik A, Pelizzari Charles A
Virginia Commonwealth University Medical Center, Richmond, Virginia 23298.
Techna Institute and the Princess Margaret Cancer Center, University Health Network, Toronto, Ontario M5G 2M9, Canada.
Med Phys. 2015 Nov;42(11):6448-56. doi: 10.1118/1.4932628.
This work presents a method of collision predictions for external beam radiotherapy using surface imaging. The present methodology focuses on collision prediction during treatment simulation to evaluate the clearance of a patient's treatment position and allow for its modification if necessary.
A Kinect camera (Microsoft, Redmond, WA) is used to scan the patient and immobilization devices in the treatment position at the simulator. The surface is reconstructed using the skanect software (Occipital, Inc., San Francisco, CA). The treatment isocenter is marked using simulated orthogonal lasers projected on the surface scan. The point cloud of this surface is then shifted to isocenter and converted from Cartesian to cylindrical coordinates. A slab models the treatment couch. A cylinder with a radius equal to the normal distance from isocenter to the collimator plate, and a height defined by the collimator diameter is used to estimate collisions. Points within the cylinder clear through a full gantry rotation with the treatment couch at 0°, while points outside of it collide. The angles of collision are reported. This methodology was experimentally verified using a mannequin positioned in an alpha cradle with both arms up. A planning CT scan of the mannequin was performed, two isocenters were marked in pinnacle, and this information was exported to AlignRT (VisionRT, London, UK)--a surface imaging system for patient positioning. This was used to ensure accurate positioning of the mannequin in the treatment room, when available. Collision calculations were performed for the two treatment isocenters and the results compared to the collisions detected the room. The accuracy of the Kinect-Skanect surface was evaluated by comparing it to the external surface of the planning CT scan.
Experimental verification results showed that the predicted angles of collision matched those recorded in the room within 0.5°, in most cases (largest deviation -1.2°). The accuracy study for the Kinect-Skanect surface showed an average discrepancy between the CT external contour and the surface scan of 2.2 mm.
This methodology provides fast and reliable collision predictions using surface imaging. The use of the Kinect-Skanect system allows for a comprehensive modeling of the patient topography including all the relevant anatomy and immobilization devices that may lead to collisions. The use of this tool at the treatment simulation stage may allow therapists to evaluate the clearance of a patient's treatment position and optimize it before the planning CT scan is performed. This can allow for safer treatments for the patients due to better collision predictions and improved clinical workflow by minimizing replanning and resimulations due to unforeseen clearance issues.
本研究提出一种利用表面成像进行外照射放疗碰撞预测的方法。本方法重点关注治疗模拟过程中的碰撞预测，以评估患者治疗位置的安全间距，并在必要时进行调整。
使用Kinect摄像头（微软公司，华盛顿州雷德蒙德）在模拟机上扫描处于治疗位置的患者及固定装置。使用skanect软件（Occipital公司，加利福尼亚州旧金山）重建表面。利用投射在表面扫描图像上的模拟正交激光标记治疗等中心。然后将该表面的点云平移至等中心，并从笛卡尔坐标转换为圆柱坐标。用平板模型模拟治疗床。使用一个半径等于从等中心到准直器板的法线距离、高度由准直器直径定义的圆柱体来估计碰撞情况。当治疗床处于0°时，圆柱体内的点在机架全旋转过程中不会碰撞，而圆柱体外的点会发生碰撞。报告碰撞角度。使用双臂上举置于α型托架中的人体模型对该方法进行了实验验证。对人体模型进行了计划CT扫描，在Pinnacle中标记了两个等中心，并将此信息导出至AlignRT（VisionRT公司，英国伦敦）——一种用于患者定位的表面成像系统。如有条件，用其确保人体模型在治疗室中的精确定位。对两个治疗等中心进行碰撞计算，并将结果与在治疗室中检测到的碰撞情况进行比较。通过将Kinect-Skanect表面与计划CT扫描的外表面进行比较，评估其准确性。
实验验证结果表明，在大多数情况下，预测的碰撞角度与在治疗室中记录的角度相差在0.5°以内（最大偏差为-1.2°）。Kinect-Skanect表面的准确性研究表明，CT外部轮廓与表面扫描之间的平均差异为2.2 mm。
该方法利用表面成像提供快速可靠的碰撞预测。使用Kinect-Skanect系统能够对患者的地形进行全面建模，包括所有可能导致碰撞的相关解剖结构和固定装置。在治疗模拟阶段使用该工具可使治疗师在进行计划CT扫描之前评估患者治疗位置的安全间距并进行优化。由于更好的碰撞预测以及通过最大限度减少因意外安全间距问题导致的重新计划和重新模拟，从而改善临床工作流程，可为患者提供更安全的治疗。
