食管癌结合锥形束CT图像引导自适应放射治疗的可行性研究

Feasibility of cone beam CT image-guided adaptive radiotherapy to treat esophageal carcinoma

目的探索利用食管癌患者首周放射治疗时的锥形束CT(cone beam computed tomography,CBCT)图像,建立个体化计划靶区以减少正常组织受照剂量的可行性。方法选取行根治三维放射治疗的食管癌患者10例,获取每位患者治疗首周前5次及后续每周治疗前CBCT验证图像,将其导入治疗计划系统中,与治疗前的定位CT图像配准融合。然后在每个CBCT图像上按患者治疗前靶区勾画原则,再次勾画临床靶区(clinic tumor volume,CTV),并根据首周治疗的摆位误差平均值外扩生成计划靶区(planning tumor volume,PTV)。将首周5个CBCT上勾画的PTV轮廓映射到定位CT上合并生成PTV1,以此法生成后续2～6周的PTV2。按照初始计划(Plan A)的参数设置,保持靶区处方剂量及各危及器官的限量要求不变,以PTV1为靶区,制定一个新的放射治疗计划,即患者个体化的自适应放射治疗计划(Plan B)。用新计划(Plan B)的95%等剂量线评估PTV2覆盖度,通过剂量-体积直方图(DVH)来比较Plan A与Plan B中肺、心脏和脊髓的受照射剂量。结果 PTV1体积比PTV体积小(P<0.05);Plan B中处方剂量95%等剂量线的覆盖率分别为:PTV1=(98.9±2.0)%和PTV2=(99.1±2.0)%,差异无统计学意义(P>0.05)。Plan B的危及器官所受剂量均小于Plan A:肺V20(25.1%vs26.9%)、平均剂量(14.0Gy vs15.1Gy),心脏的平均剂量(16.7Gy vs19.7Gy)和脊髓最大剂量(42Gy vs43Gy),差异具有统计学意义(P<0.05)。结论利用患者治疗首周CBCT图像资料反馈的信息,可以有效减少计划靶区体积。修改后的计划可在后续治疗中开展,并能进一步减少靶区周围危及器官的照射剂量和潜在提高靶区剂量。

Objective To investigate the feasibility of reducing the exposure dose on normal tissue by creating a specific planning target volume（PTV） using cone beam computed tomography （CBCT） imaging during the first week of radiotherapy in patients with esophageal carcinoma. Methods Ten patients with esophageal carcinoma treated by radical radiotherapy were investigated.CBCT im- ages were acquired on clays 1-5 of the first week of radiotherapy and once a week later.The images were imported into the planning system and matched with the planning CT for the same treatment position.The same tumor and esophagus as in the initial plan（plan A ） for the length of the clinic target wlume（CTV） were contoured on each CBCT image.Then CTV was contoured again on each CBCT image according to the plan prior to radiotherapy. The PTV was defined as CTV（tumor,nodes） plus setup error,which was acquired during the first weeks of treatment.A composite volume（PTV1 ） was created by combining the five CBCT volumes in the first week.PTV2 was generated in the same way using the five CBCT volumes of weeks 2-6.An adaptive plan（plan B） was formulated based on the PTV1 target in order to maintain the same radiation planning parameters and target prescription dose as in plan A,while limiting the exposure dose to organs at risk.Coverage of the 95% prescription isodose was evaluated on PTV1 and PTV2 with the same radiation planning.Dose-volume histograms（DVHs） for lung, heart and spinal cord of the two plans were compared. Results For the adaptive plan,the coverage of the 95% prescription isodose for PTV1 was 95.5±3.4%（P=0.001 ）,while for PTV2 it was 99.1±1.7% （P=0.001）.Several parameters with plan B were significantly smaller than with plan A （P〈0.05）：lung V20 （25.1% vs 26.9%） and mean dose （14.1Gy vs 15.1Gy）,heart mean dose （26.9Gy vs 20.7Gy） and spinal cord maximum dose （41.5Gy vs 42.9Gy）. Conclusions A reduced planning volume can be constructed based on CBCT images acquired during the first week of radiotherapy.The modified plan can be implemented in the follow-up treatment,considerably reducing the dosage on organs around the target area and potentially increasing the dosage on the target.