胸上段食管癌调强放疗摆位误差及靶区外扩距离研究

The setup errors and reasonable target margin in radiotherapy of superior chest segment esophageal carcinoma

目的 应用千伏级锥形束CT测量胸上段食管癌患者放疗摆位误差并估测临床靶体积至计划靶体积（CTV→PTV）外扩距离.方法 选择2010-2012年间13例胸上段食管癌患者的调强放疗计划CT图像,将图上CTV外扩形成内靶体积（ITⅣ）,再将ITV逐步1 mm/次外扩10次,每例患者均形成10个大小不一的PTV.根据这些PTV制定计划并模拟摆位误差.找到一合适PTV,使在有摆位误差时仍能保证95％ ITy达到处方剂量,从而得到CTV→PTV外扩距离.结果 摆位误差在上下方向上最大,为（3.42±2.19） mm.通过PTV外扩法测得ITV→PTV的外扩范围为5mm.根据PTV外扩法所得外扩距离制定的新计划与原计划相比双肺V5、脊髓D1cm3分别增加0.87％、4.95 Gy,心脏V40、PTV D95、PTV V1oo、ITV D95、ITV V1oo分别减少0.62％、4.95 Gy、8.38％、1.84 Gy、1.87％.结论 通过PTV外扩法测得胸上段食管癌患者CTV→PTV在左右、上下、前后方向上的外扩范围分别为7、8、7 mm.

Abstract： Objective To investigate the setup errors of super chest segment of esophageal cancer patients before radiotherapy delivery by KV cone beam CT,and evaluate the margin from CTV to PTV.Methods From 2010 to 2012,13 patients with super chest segment of esophageal cancer whose IMRT planning CT images were included in this study.Delineate target on the CT images of treatment planning and enlarge the margin of CTV to form ITV,then enlarge the margin of ITV gradually 10 times by 1 mm each time to form varied PTV,and create the plan according to the size of the PTV,simulate setup errors in the new plan to obtain the simulation of the actual exposure curve and find a suitable PTV to assure 95% ITV volume as ever to approach the prescription dose,obtained the outside enlarge distance of CTV → PTV.Results The maximum setup errors in the direction of the anterior and posterior positioning was （3.42 ±2.19） mm.The margin of ITV→PTV is 5 mm which was figured out by PTN enlarging method.Compared to the original plan that under the condition of draw up the radiotherapy plan that based on the method of PTV enlarging obtained the CTV→PTV and simulate the actual dose distribution according to the setup errors：total lung V5,spinal cord D1cm3,increased by about 0.87%,4.95 Gy,heart V40,PTV D95,PTV V100,ITV D95,ITV V100 were reduced about 0.62%,4.95 Gy,8.38%,1.84 Gy,1.87%,all of them have statistically difference.Conclusions Range of external expansion of the left to right,superior to inferior and anterior to posterior is 7 mm,8 mm and 7 mm respectively,according to the method of PTV enlarging obtained the margin of CTV→PTV of super chest segment of esophageal cancer patients.