中上段食管癌图像引导放疗中摆位误差及靶区外放边界的确定

Evaluations of set-up errors and target margins for super and middle part of esophageal carcinoma in image guided radiotherapy

目的 应用锥形束CT（CBCT）测量食管癌调强放疗的摆位误差,从而确定靶区外放距离;分析不同的靶区外放距离对肺和脊髓正常组织的影响.方法 选择2012年12月至2013年12月的12例中上段食管癌患者,根据每周1次CBCT所得的60组测量数据确定患者左右、头脚以及前后方向的摆位误差,根据实际测量的摆位误差结果以及靶区运动大小得出靶区外放距离,针对临床靶区CTV外放5 mm得到的计划靶区PTV以及根据实际测量摆位误差外放得到的计划靶区PTV分别制定调强治疗计划,在保证计划靶区PTV覆盖率相同（V95≥95％）的情况下对两种计划的危及器官受量进行比较和统计学分析,评价参数包括双肺的V5、V20、V30、平均剂量Dmean以及脊髓受量D1cm3.结果 食管癌调强放疗在左右、头脚以及前后3个方向的摆位误差分别是（2.02±1.74）、（2.02±1.93）、（2.03±1.89）mm.上段食管癌由临床靶区（CTV）到计划靶区（PTV）的外放距离为左右4.7 mm、头脚8.5 mm、前后5.6 mm;中段食管癌为左右5.0 mm、头脚11.0 mm、前后6.2 mm.两种计划比较,双肺的V5、V20、V30、平均剂量Dmean和脊髓受量D1cm3的差异有统计学意义（t=-8.23、-5.55、-4.66、-6.87、-4.67,P＜0.05）.结论 根据CBCT测量结果确定摆位误差以及文献报道结果得出食管癌靶区外放边界,对于临床治疗有一定的参考意义.

Objective To investigate the set-up errors of super and middle part of esophageal cancer patients using cone-beam CT （CBCT） during intensity modulated radiotherapy （IMRT）,hence determine various margins from CTV to PTV.The corresponding influence on the normal tissues （lung and spinal cord） was also discussed.Methods From December 2012 to December 2013,12 patients with upper and middle segment of esophageal cancer were chosen.Using their 60 sets of weekly acquired CBCT images prior to the treatment,the lateral,longitudinal,and vertical set-up errors of each patient were obtained.Based on these measured errors and the target motions,we adopted new margins to create new PTV.Then IMRT plans were created for the original PTV （5 mm margin in all directions on CTV） and new PTV respectively.On condition of the same target coverage （V95 ≥ 95％）,the doses to lungs （V5,V20,V30,D） and spinal cord （D1 cm3） were compared statistically between the original and new plans.Results According to the 60 CBCT scans,the average left-right （RL）,superior-inferior （SI）,anterior-posterior （AP） set-up errors were （2.02 ± 1.74）,（2.03 ± 1.93）,and （2.02 ± 1.89） mm respectively.The margins were 5.6 mm （RL）,8.5 mm （SI）,and 4.7 mm （AP） for the upper esophagus and 6.2 mm （RL）,11 mm （SI）,and 5.0 mm （AP） for the middle esophagus.Comparison of both lungs and spinal cord suggested significant differences between the two plans （t =-8.23,-5.55,-4.66,-6.87,-4.67,P ＜0.05）.Conclusions The margins from CTV to PTV should be created via CBCT-measured set-up errors and previous reports,which can be helpful for clinical treatment.