基于深度相机的三维点云放疗实时监测系统的研发与应用

Development and application of three-dimensional point cloud radiotherapy real-time monitoring system based on depth camera

目的利用深度相机开发三维点云放疗实时监测系统并验证其可行性。方法以深度相机坐标系为世界坐标系,由校准模体得到定位CT坐标系与世界坐标系之间的转换关系。患者的定位CT点云经上述关系转换到世界坐标系中并与深度相机实时获取的患者表面点云配准计算六维误差,完成摆位验证及放疗中分次内体位误差监测。统计系统六维计算误差的均值、标准差,配准后点云的豪斯多夫距离以及各部分程序运行时间,验证系统的可行性。选取15例真实患者,统计本系统与锥形线束CT之间六维误差。结果模体实验中,系统在左右、头脚、腹背方向的误差分别为(1.292±0.880)、(1.963±1.115)、(1.496±1.045)mm,在偏转、俯仰、翻滚角度的误差分别为0.201°±0.181°、0.286°±0.326°、0.181°±0.192°。对于真实患者,系统平移误差在2.6 mm以内,旋转误差在1°左右,程序运行1~2帧/s,精度和速度满足放疗要求。结论基于深度相机的三维点云放疗实时监测系统能自动完成放疗前摆位验证、放疗中体位实时监测,并提供误差视觉反馈,具有潜在的临床应用价值。

Objective To develop the real-time radiotherapy monitoring system of three-dimensional(3D)point cloud by using depth camera and verify its feasibility.Methods Taking the depth camera coordinate system as the world coordinate system,the conversion relationship between the simulation CT coordinate system and the world coordinate system was obtained from the calibration module.The patient's simulation CT point cloud was transformed into the world coordinate system through the above relationship,and registered with the patient's surface point cloud obtained in real-time manner by the depth camera to calculate the six-dimensional(6D)error,and complete the positioning verification and fractional internal position error monitoring in radiotherapy.Mean and standard deviation of 6D calculation error,Hausdorff distance of point cloud after registration and the running time of each part of the program were calculated to verify the feasibility of the system.Fifteen real patients were selected to calculate the 6D error between the system and cone beam CT(CBCT).Results In the phantom experiment,the errors of the system in the x,y and z axes were(1.292±0.880)mm,(1.963±1.115)mm,(1.496±1.045)mm,respectively,and the errors in the rotation,pitch and roll directions were 0.201°±0.181°,0.286°±0.326°,0.181°±0.192°,respectively.For real patients,the translational error of the system was within 2.6 mm,the rotational error was approximately 1°,and the program run at 1-2 frames/s.The precision and speed met the radiotherapy requirement.Conclusion The 3D point cloud radiotherapy real-time monitoring system based on depth camera can automatically complete the positioning verification before radiotherapy,real-time monitoring of body position during radiotherapy,and provide error visual feedback,which has potential clinical application value.