脑转移瘤立体定向放疗分次间和分次内摆位误差及残余误差分析

摘要

Objective To evaluate the necessity of arc by arc setup verification in patients with brain metastases receiving stereotactic radiotherapy (SRT) by analyzing the inter-and intra-fraction setup errors and residual errors collected from the ExacTrac X-ray portal image.Methods Clinical data of brain metastases patients treated with SRT in the previous two years were retrospectively analyzed.The ExacTrac X-ray setup images were collected after the normal setup procedure.Setup errors were calculated by registering the cranial bony structures of the ExacTrac X-ray setup images to that of the digitally reconstructed setup images.The inter-and intra-fraction setup errors and residual errors were statistically analyzed.Results Seventy-five patients from 116 lesions received 337 cycles of SRT of the head.The inter-and intra-fraction translational setup errors in the x,y and z directions were (0.93±0.86) mm and (0.15±0.59) mm;(1.83± 1.27) mm and (0.25±0.73) mm;(0.96±0.80) mm and (0.14±0.56) mm,respectively.The inter-and intra-fraction rotational setup errors in the x,y,z directions were (0.65°± 0.62°) and (0.19°± 0.40°);(0.97°±0.94°) and (0.13°± 0.25°);(0.92°± 0.71°) and (0.10°± 0.29°),respectively.The residual translational setup errors in the x,y,z directions were (0.06±0.23) mm,(0.08±0.24) mm and (0.08±0.22)mm,and (0.12°± 0.27°),(0.09°± 0.18°) and (0.06°± 0.19°) for the residual rotational setup errors,respectively.For a reference setup error threshold of 0.7 mm/0.7°,99.1％ of the SRT exceeded the threshold and required setup correction.For 1 006 non-coplanar arcs,rotating the treatment couch from 0° to the treatment angle made 66.4％ of arcs exceed the threshold and require at least once setup correction.Conclusions During SRT for brain metastasis,the inter-and intra-fraction setup errors should be emphasized.It is necessary to perform arc by arc setup error verification.%目的:分析脑转移患者立体定向放疗ExacTrac X线图像,计算分次间和分次内摆位误差及残余误差,分析进行逐弧位置验证的必要性.方法:通过对过去2年在本中心采用头部立体定向放疗的脑转移瘤病例的回顾性分析,配准其数字重建图像和ExacTrac正交kV级验证图像,计算患者3个方向的平移误差和旋转误差.数据包含分次间摆位误差、分次内摆位误差和残余误差.结果:75例1 16个病灶进行了337次头部立体定向放疗.分次间、分次内平移摆位误差分别为左右方向x(0.93±0.86)、(0.15±0.59) mm,头脚方向y(1.83±1.27)、(0.25±0.73) mm,腹背方向z(0.96±0.80)、(0.14±0.56) mm;分次间、分次内旋转摆位误差分别为矢状面Rx (0.65°±0.62°)、(0.19°±0.40°),横断面Ry (0.97°±0.94°)、(0.13°±0.25°),冠状面Rz (0.92°±0.71°)、(0.10°±0.29°).残余平移误差左右、头脚、腹背方向分别为(0.06±0.23)、(0.08±0.24)、(0.08±0.22) mm;残余旋转误差矢状面、横断面、冠状面分别为(0.12°±0.27°)、(0.09°±0.18°)、(0.06°±0.19°).337次分次间摆位误差99.1％超过误差阈值(0.7 mm,0.7°)需要至少校正1次;1 006组分次内摆位误差33.6％在治疗床转到位验证无需误差校正,66.4％需要校正至少1次.结论:头部立体定向放疗患者要重视分次间摆位误差和分次内摆位误差,进行逐弧体位验证是非常必要的.