锥形束CT引导下胸上段食管癌摆位误差及计划靶区外放边界研究

Analysis of the upper segment esophageal setup errors and planning target margin based on CBCT for esophageal radiation with thermoplastic film immobilized

目的研究锥形束CT调强治疗胸上段食管癌患者的摆位误差,推算其靶区外放边界。方法采用瓦里安iX TM直线加速器治疗胸上段食管癌40例。所有入组患者均常规摆位后行CBCT,治疗床在线校正后,再次CBCT,治疗结束后再次CBCT。分别获取摆位后、治疗前、治疗后X射线容积影像,所有容积图像采用自动骨性和手动微调的配准方式与计划CT配准后,即可获得患者前后(腹背)、左右、上下(头脚)误差,分析摆位误差及PTV的外放边界。结果患者扫描CBCT共计956次,所有入组患者分次间上下、左右、前后误差均减小(Pearson=-0. 523,-0. 511,-0. 562,P <0. 05),全组患者摆位误差在左右(x)、上下(y)、前后(z)方向分别为(0. 22±2. 94)、(1. 51±3. 22)、(-1. 89±1. 38) mm,由公式计算出CTV在x、y、z方向分别需外放5. 16、5. 87、4. 52 mm。结论锥形束CT可明显减小胸上段食管癌患者的摆位误差,从而为缩小CTV的外放边界提供依据。

Objective To evaluate the setup errors for the upper segment esophageal cancer with cone beam CT（ CBCT） in esophageal patients immobilized by thermoplastic film,and to probe the margins from the esophageal clinical target volume（ CTV） in 3 directions. Methods A total of 40 patients treated by Varian i XTM Linear accelerator with upper segment esophageal cancer were enrolled. During the treatment,a CBCT was acquired on a daily basis after conventional position and was registered to the planning CT to determine initial inter-fraction error. Then a second CBCT scan was performed to calculate residual inter-fraction error after the couch online correction. After the RT delivery,a final CBCT was acquired to assess intra-fraction motion. Results A total of 956 CBCT images were acquired from 40 patients. After couch online correction,the inter-fractional setup errors in x y z were significantly reduced（ Pearson =-0. 523,-0. 511,-0. 562,P〈 0. 05）. The setup errors on（ left-right）,（ superior-inferior）,（ anterior-posterior） translational directions were（ 0. 22 ± 2. 94） mm,（ 1. 51 ± 3. 22） mm,（-1. 89 ± 1. 38） mm,and the margins from CTV were recommended as not less than 5. 16 mm,5. 87 mm,4. 52 mm in,and direction,respectively. Conclusion For the upper segment esophageal cancer patients immobilized by thermoplastic film,which recommended to reduce the external boundary of CTV,respectively. The position immobilized method and the positioning workflow should be further improved in order to reduce the influence of breathing movement on setup errors.