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目的:建立光学表面监测系统(OSMS)在头部无框架立体定向放射外科(SRS)和立体定向放射治疗(SRT)中应用的基本流程，评价OSMS在头部模体和应用Q-Fix开孔面罩固定的头部SRT患者中，分次内实时监测位置误差的精确性和有效性。方法:通过头部SRS仿真模体OSMS的监测位移与Edge六维床预设位移的偏差，评估OSMS实时监测运动偏差，及在治疗床非零角度和其中一组摄像头被加速器旋转机架遮挡的情况下，OSMS监测头部运动的能力。同时本研究选取10例50分次接受头部无框架SRT治疗的患者，所有患者经Q-Fix开孔面罩固定并整个治疗分次内应用OSMS监控，通过分析离线日志文件获得OSMS实时监测的分次内误差；患者治疗后行锥形束CT(CBCT)扫描，获得六维度误差作为CBCT验证的分次内误差。结果:模体研究中，OSMS监测偏差与预设位移在六维度方向均有较强相关性；治疗床与机架0°时，OSMS探测的平移方向和旋转角度的三维矢量偏差分别为(0.28±0.10) mm和(0.15±0.09)°；有一组摄像头被遮挡的情况下，平移和旋转方向的三维矢量偏差分别为(0.35±0.13) mm和(0.17±0.09)°；床非0°时OSMS监测偏差值均大于床0°偏差值，床270°时三维矢量偏差最大，分别为平移方向(0.69±0.19)mm和旋转角度(0.32±0.12)°。在Q-fix开孔面罩固定的SRT患者中，OSMS与CBCT监测的分次内运动幅度差异较小，平移方向三维矢量偏差分别为(0.40±0.26)mm和(0.29±0.10)mm；旋转方向三维矢量偏差分别为(0.33±0.20)°和(0.26±0.08)°。结论:OSMS是一种有效的光学引导放射治疗工具，OSMS的分次内实时运动监测功能具有亚毫米级精度，可以实现分次内误差的精确监控。为保障无框架头部SRS/SRT治疗精确实施，有必要联合OSMS进行分次内位置监控。“,”Objective:To establish a novel clinical application process of the optical surface monitoring system (OSMS) in the cranial frameless stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT), and to assess the accuracy and effectiveness of the OSMS in the intra-fraction motion monitoring of both cranial phantoms and cranial SRT patients fixed using the Q-Fix encompass immobilization system.Methods:The deviations of OSMS in the real-time motion monitoring were assessed by determining the deviations between the displacement of the cranial SRS phantoms detected by the OSMS and the predefined displacement of the Varian Edge six degrees of freedom (6DoF) couch. The ability of the OSMS to conduct real-time monitoring of the head movement was also analyzed when one camera was blocked by the rotary gantry of the accelerator and when the couch was at non-zero angles. Moreover, ten patients who received 50 fractions of cranial frameless SRT were enrolled in this study. All the patients were fixed using the Q-Fix Encompass system, and their intra-fraction motion was monitored using the OSMS. The intra-fraction errors of OSMS real-time monitoring throughout the treatment were obtained from the OSMS logs. The patients received cone-beam computed tomography (CBCT) after the beam delivery, and the six-dimensional errors were obtained as intra-fraction motion errors of the CBCT.Results:For the cranial phantoms, there was a close correlation between the OSMS monitoring deviations and the predefined displacement in six dimensions. The OSMS-detected 3D vector deviations in the translational and rotational directions were (0.28±0.10) mm and (0.15±0.09)°, respectively when the angel both the gantry and couch was 0° and were (0.35±0.13) mm and(0.17±0.09)°, respectively, when one camera was blocked. The OSMS monitoring deviations with the couch at a non-zero degree were greater than those at zero degree. The maximum deviations occurred when the couch was at 270° and were (0.69±0.19) mm and (0.32±0.12)°, respectively, in the translational and rotational directions. For the cranial SRT patients fixed using the Q-Fix Encompass system, the OSMS and CBCT showed comparable intra-fractional motion deviations, which were (0.40±0.26) and (0.29±0.10) mm, respectively in the translational direction and were (0.33±0.20)°and (0.26±0.08)° in the rotational direction.Conclusions:The OSMS is an effective tool for optically guided radiotherapy, which allows for intra-fraction real-time motion monitoring with sub-millimeter accuracy. Therefore, to ensure the accurate preformation of cranial SRS/SRT, it is necessary to conduct the intra-fractional position monitoring using OSMS.