CREATIS, CNRS UMR 5220, INSERM U1044, Université Lyon 1, INSA-Lyon, Villeurbanne, France.
Phys Med Biol. 2012 Jan 21;57(2):357-73. doi: 10.1088/0031-9155/57/2/357. Epub 2011 Dec 14.
Real-time optical surface imaging systems offer a non-invasive way to monitor intra-fraction motion of a patient's thorax surface during radiotherapy treatments. Due to lack of point correspondence in dynamic surface acquisition, such systems cannot currently provide 3D motion tracking at specific surface landmarks, as available in optical technologies based on passive markers. We propose to apply deformable mesh registration to extract surface point trajectories from markerless optical imaging, thus yielding multi-dimensional breathing traces. The investigated approach is based on a non-rigid extension of the iterative closest point algorithm, using a locally affine regularization. The accuracy in tracking breathing motion was quantified in a group of healthy volunteers, by pair-wise registering the thoraco-abdominal surfaces acquired at three different respiratory phases using a clinically available optical system. The motion tracking accuracy proved to be maximal in the abdominal region, where breathing motion mostly occurs, with average errors of 1.09 mm. The results demonstrate the feasibility of recovering multi-dimensional breathing motion from markerless optical surface acquisitions by using the implemented deformable registration algorithm. The approach can potentially improve respiratory motion management in radiation therapy, including motion artefact reduction or tumour motion compensation by means of internal/external correlation models.
实时光学表面成像系统提供了一种非侵入性的方法，可在放射治疗过程中监测患者胸部表面的分次内运动。由于在动态表面采集过程中缺乏点对应关系，因此此类系统目前无法像基于被动标记的光学技术那样，在特定的表面标志点提供 3D 运动跟踪。我们建议应用可变形网格配准从无标记光学成像中提取表面点轨迹，从而生成多维呼吸轨迹。所研究的方法基于迭代最近点算法的非刚性扩展，使用局部仿射正则化。通过使用临床可用的光学系统在三个不同呼吸阶段分别对获取的胸腹部表面进行两两配准，在一组健康志愿者中定量评估了跟踪呼吸运动的准确性。在呼吸运动主要发生的腹部区域，运动跟踪的准确性最高，平均误差为 1.09 毫米。结果表明，通过使用所实现的可变形配准算法，从无标记的光学表面采集中恢复多维呼吸运动是可行的。该方法有望通过内部/外部相关模型来改善放射治疗中的呼吸运动管理，包括减少运动伪影或肿瘤运动补偿。
