Delombaerde Laurence, Petillion Saskia, Michiels Steven, Weltens Caroline, Depuydt Tom
Department of Radiation Oncology, University Hospitals Leuven, Herestraat 49, Leuven 3000, Belgium.
Department of Oncology, KU Leuven, Herestraat 49, Leuven 3000, Belgium.
Phys Imaging Radiat Oncol. 2019 Jul 25;11:21-26. doi: 10.1016/j.phro.2019.07.003. eCollection 2019 Jul.
Current commercial surface scanning systems are not able to monitor patients during radiotherapy fractions in closed-bore linacs during adaptive workflows. In this work a surface scanning system for monitoring in an O-ring linac is proposed.
A depth camera was mounted at the backend of the bore. The acquired surface point cloud was transformed to the linac coordinate system after a cube detection calibration step. The real-time surface was registered using an Iterative Closest Point algorithm to a reference region-of-interest of the body contour from the planning CT and of a depth camera surface acquisition from the first fraction. The positioning accuracy was investigated using anthropomorphic 3D-printed phantoms with embedded markers: a head, hand and breast. To simulate clinically observed positioning errors, each phantom was placed 24 times with 0-10 mm and 0-8° offsets from the planned position. At every position a cone-beam CT (CBCT) was acquired and a surface registration performed. The surface registration error was determined as the difference between the surface registration and the CBCT-to-CT fiducial marker registration.
The registration errors were (mean ± SD): lat: 0.4 ± 0.8 mm, vert: -0.2 ± 0.2 mm, long: 0.3 ± 0.5 mm and Yaw: -0.2 ± 0.6°, Pitch: 0.4 ± 0.2°, Roll: 0.5 ± 0.8° for the body contour reference, and lat: -0.7 ± 0.7 mm, vert: 0.3 ± 0.2 mm, long: 0.2 ± 0.5 mm and Yaw: -0.5 ± 0.5°, Pitch: 0.1 ± 0.3°, Roll: -0.7 ± 0.7° for the captured surface reference.
The proposed single camera intra-bore surface system was capable of accurately detecting phantom displacements and allows intrafraction motion monitoring for surface guided radiotherapy inside the bore of O-ring gantries.
目前的商业表面扫描系统无法在自适应工作流程中对封闭孔径直线加速器放疗分次过程中的患者进行监测。在本研究中，我们提出了一种用于在O形环直线加速器中进行监测的表面扫描系统。
在孔径后端安装一个深度相机。在进行立方体检测校准步骤后，将获取的表面点云转换到直线加速器坐标系。使用迭代最近点算法将实时表面与计划CT中的身体轮廓参考感兴趣区域以及首次分次的深度相机表面采集结果进行配准。使用带有嵌入式标记的拟人化3D打印体模（头部、手部和乳房）研究定位精度。为了模拟临床观察到的定位误差，每个体模从计划位置偏移0 - 10毫米和0 - 8°放置24次。在每个位置采集锥形束CT（CBCT）并进行表面配准。表面配准误差定义为表面配准与CBCT到CT基准标记配准之间的差值。
对于身体轮廓参考，配准误差为（平均值±标准差）：横向：0.4±0.8毫米，纵向： - 0.2±0.2毫米，前后：0.3±0.5毫米，偏航： - 0.2±0.6°，俯仰：0.4±0.2°，滚动：0.5±0.8°；对于捕获的表面参考，横向： - 0.7±0.7毫米，纵向：0.3±0.2毫米，前后：0.2±0.5毫米，偏航： - 0.5±0.5°，俯仰：0.1±0.3°，滚动： - 0.7±0.7°。
所提出的单相机孔径内表面系统能够准确检测体模位移，并允许在O形环龙门架孔径内进行表面引导放疗的分次内运动监测。
