图像引导调强放疗在食管癌治疗的应用

目的探讨食管癌影像引导的放射治疗(image guided radiation therapy,IGRT)中的摆位误差对靶区和危及器官物理剂量变化的影响。方法选择2010年9月—2011年11月我院用美国瓦里安公司的具有机载影像系统(on-borad-imager,OBI)的23EX直线加速器治疗机治疗食管癌患者28例。所有患者在首次摆位后、摆位误差纠正后及治疗后,用KV级的锥形束CT(cone beam CT,CBCT)扫描获取患者的3种容积图像,每位患者每周验证1次,采集3次CBCT图像。28例患者共扫描411次。每例患者的每次CBCT图像均与其原始计划CT图像进行靶中心匹配,计算首次摆位后、摆位误差纠正后及治疗后在X(左右)、Y(腹背)、Z(头脚)方向偏移误差,获得3组X、Y、Z三维方向的移床数据。将每位患者每次CBCT校正的偏移误差,通过Eclip se 8.6Version治疗计划系统研究摆位误差在食管癌放疗中对靶区和危及器官剂量分布的影响。结果 (1)28例食管癌患者每次首次摆位后的CBCT共137次,系统误差±随机误差在X、Y、Z方向分别为(0.696 3±2.794 7)、(0.688 9±2.250 9)、(0.859 3±3.425 5)mm,对这些摆位误差均进行实时纠正,纠正后X、Y、Z 3个方向摆位误差的系统误差和随机误差均低于首次摆位误差。(2)摆位误差纠正前、纠正后的数据比较差异有统计意义(P<0.05),摆位误差纠正后与治疗后相比差异无统计学意义(P>0.05)。(3)计算模拟得出原发肿瘤(GTV)平均剂量变化为-3.52%～2.44%,心脏剂量变化为-4.18%～25.53%,肺脏剂量变化为-1.82%～13.93%,脊髓剂量变化为-10.50%～20.87%。结论采用IGRT对食管放疗的摆位误差纠正有明显的作用,且能较大幅度减少摆位误差。应用OBI-CBCT系统,进行实时摆位误差校正,使靶区及周围正常组织器官剂量分布准确,提高靶区剂量而减少正常组织的受量,为临床放疗提供质量保证。

Application of image-guided radiotherapy in esophageal carcinoma

Objective To explore the effect of the setup error on the physics dose distribution of targets and peripheral organs at risk(OAR) undergoing the Esophageal′ IGRT(image guided radiation therapy).Methods Twenty-four cases of esophageal carcinoma were included in this study from September 2010 to November 2011 by the synergy 23EX linear accelerator of the On-Borad-Imager by Varian.All patients were accepted three kinds of CBCT(Cone Beam CT) scans: one before therapy,one after rectification and one was obtained after therapy.3CBCT scans were collected every week for one patient and there were 28 patients received CBCT scans A total of 140 CBCT scans were obtained,which were matched with the original plan CT images through target center.Calculated the error after initial setup,after re-positioning and after radiation delivery in X(left-right),Y(anterior-posterior) and Z(head-foot) direction.Noted all the setup errors.Then the treatment planning system of Eclip se8.6 version was used to study the effects of the setup error on the dose distribution undergoing the radiation therapy for esophageal carcinoma.Results(1) Twenty eight patients received a total of 137 CBCT scans after initial setup.The systematic±random error in X,Y and Z direction was(0.696 3±2.794 7),(0.688 9±2.250 9) and(0.859 3±3.425 5) mm,respectively.All the setup errors were corrected,and after the correction,both the systematic errors and random errors were obviously lower than those before correction.(2) The difference of the setup error between before therapy and after rectification was statistically significant(P<0.05).The difference of the setup error between after rectification and after therapy was no significant difference(P>0.05).(3) The extent of dose variation for GTVnx,heart,lung,spinal cord was-3.52%~2.44%,-4.18%~25.53%,-1.82%~13.93% and-10.50%~20.87%.Conclusion IGRT has a conspicuous effect on rectificating set-up errors of radiotherapy for esophageal carcinoma and reduces the setup error obviously.The OBI-CBCT system could revise the setup error in real time,which could reduce the systematic and random error and improve the accuracy of setup and dose of targets and OAR.As a result,it could provide better quality assurance in radiation therapy.