光学引导跟踪系统在放疗应用中的准确性研究

Accuracy of the optically guided tracking system in radiotherapy

目的初步探究体表光学引导跟踪系统(OGTS)在肿瘤放射治疗应用中的追踪精度。方法分为模体验证及临床验证,模体验证采用专用设备,利用OGTS记录光学标记点在反光球平台上从指定位置移动到目标位置的位移值,将该位移值与模体中固定距离比较,以计算系统的准确性与重复性。临床验证通过选取45例放疗患者进行OGTS跟踪准确性和重复性研究,其中头部、乳腺、直肠肿瘤患者各15例。每例患者均获取随机3个治疗分次下图像引导校正摆位前后图像引导定位系统(IGPS)和OGTS的值,分别记录每次误差校正的平移值。治疗前用IGPS修正患者摆位误差并获取相关数据,以IGPS校正平移误差的结果为金标准验证OGTS监测患者位置平移的准确性,计算综合平移偏差。结果模体测量结果显示,跟踪准确性的综合平移偏差最大值为0.18 mm,跟踪重复性综合平移偏差的标准差为0.03 mm。临床试验结果统计显示,IGPS与OGTS追踪精度仅在头部z方向上差异有统计学意义(t=2.21,P<0.05),而在头部其他方向及乳腺、直肠的3个平移方向差异均无统计学意义(P>0.05)。综合平移偏差分析表明,在头、乳腺、直肠分别为(0.91±0.62)、(1.64±1.30)和(1.52±1.29)mm,符合两者偏差≤2 mm的要求。结论OGTS操作简单、追踪精度较好,可辅助IGPS用于治疗中实时呼吸监测。

Objective To explore the tracking accuracy of the surface optically guided tracking system(OGTS)in radiotherapy.Methods Phantom verification and clinical trial verification were adopted.Specialized equipment was employed for the phantom verification.Specifically,the displacement of the optical markers as they moved from a predetermined position to the target position on the reflector ball platform was captured using the OGTS,and then the obtained displacement was compared with the fixed distance within the phantom to calculate the accuracy and repeatability of the OGTS.For the clinical trial verification,45 patients treated with radiotherapy,which consisted of 15 cases with head,breast,and rectal tumors each,were selected to investigate the tracking accuracy and repeatability of the OGTS.For each patient,the values derived from the image-guided positioning system(IGPS)and the OGTS before and after image-guided setup error correction during three times of fractionated radiotherapy were randomly obtained.The translational errors of each error correction were also recorded.Before radiotherapy,patients′setup errors were corrected and relevant data were obtained using the IGPS.The correction result of translation errors obtained using the IGPS served as a gold standard to verify the accuracy of the OGTS in monitoring the translational motion of patients.Finally,the comprehensive translational deviation of both method was calculated.Results The phantom measurements showed that the comprehensive translational deviation for tracking accuracy and tracking repeatability of the OGTS had a maximum deviation and a standard deviation of 0.18 mm and 0.03 mm,respectively.The clinical trial result indicated that the tracking accuracy of IGPS and OGTS exhibited statistically significant differences only for the head in the z direction(t=2.21,P<0.05).Conversely,no statistically significant differences were observed for the head in the remaining directions or for the breast and rectum in the three translational directions(P>0.05).The analysis showed that comprehensive translational deviations for the head,breast,and rectum derived from OGTS and IGPS were(0.91±0.62),(1.64±1.30),and(1.52±1.29)mm,respectively,satisfying the requirement that the deviations should be below 2 mm.Conclusions The OGTS,featuring easy operation and high tracking accuracy,can assist the IGPS in real-time respiratory monitoring during radiotherapy.