胸段食管癌IGRT中摆位误差分析

摘要

目的 使用CBCT测量食管癌IGRT中的摆位误差,为ART开展提供基础数据.方法 使用千伏级CBCT采集23例胸段食管癌治疗前、后摆位图像,探讨配准方法、病变部位以及不同治疗时间IGRT前摆位误差变化.单因素方差分析不同治疗时间的差异.结果 骨性及灰度匹配在x、z轴测量摆位误差有显著差异.不使用CBCT下PTV在x、y、z轴向胸上段癌分别外扩6、17、6 mm,胸中段癌分别外扩4、17、6 mm,胸下段癌分别外扩11、11、4 mm.每次使用CBCT行疗前摆位误差纠正则x、y、z轴向分别外扩2、2、4 mm.不同治疗时间IGRT前摆位误差在y轴上相近(P=0.858),在x、z轴上自第5周开始IGRT前摆位误差均高于其他几周(P=0.001,P=0.000).结论 胸段食管癌IGRT中建议采用灰度配准.不同部位食管癌PTV在x、y、z轴向外扩范围应有所不同.IGRT可使PTV外放边界显著缩小.疗前期摆位误差可考虑用于指导后续治疗,治疗后期患者x、z轴向疗前摆位误差变大,建议自第5周时更换体膜进行模拟定位,重新制定治疗计划.%Objective The purpose of the study was to use cone beam CT (CBCT) scans to evaluate setup errors in image-guided radiotherapy with thoracic esophageal carcinoma,in order to refer for adaptive radiotherapy.Methods CBCT scans were performed before and at the end of image-guided radiotherapy with 23 thoracic esophageal carcinoma patients.The registration method and setup error in different lesions and treatment weeks were measured.The difference of treatment time was single factor analysis of variance.Results Compared with bone registration and gray value registration,the setup errors in x and z axis have significant differences.Without CBCT,the adequate coverage margins required for the CTV in x,y and z axis with upper,middle and lower esophageal carcinoma were 6 mm,17 mm,6 mm;4 mm,17 mm,6 mm and 11 mm,11 mm 4 mm,respectively.The adequate coverage margins of the plan target volume (PTV) were 2 mm,2 mm and 4 mm in x,y and z axis if the CBCT was applied in irradiation during the image guided radiotherapy.When compared with setup errors at different weeks,no significant difference was found among them in y axis (P =0.001,0.000),but the setup errors of the fifth week in x and z axis were larger significantly than those of other weeks (P =0.858).Conclusions Gray value registration is recommended in image-guided radiotherapy with thoracic esophageal carcinoma.The adequate coverage margins are different in x,y and z axis with different lesions.The coverage margin of the PTV could be reduced significantly as CBCT are applied during the irradiation.The setup errors measured during earlier treatment period can be considered to guide subsequent irradiation.The setup errors in x and z axis become larger during the later irradiation course.Re-simulation should be recommended at the the fifth treatment week.