利用CBCT联合六自由度治疗床研究宫颈癌术后放疗摆位误差及CTV外放边界

目的 利用千伏级CBCT联合HexaPOD evo RT六自由度治疗床研究宫颈癌术后盆腔放疗摆位误差,推算CTV外放边界。方法 采用医科达AXESSE^TM直线加速器治疗宫颈癌术后患者17例。所有患者常规摆位后CBCT,治疗床在线校正后再次CBCT,治疗后再次CBCT,分别获得XVI。与计划CT图像配准后,即可获得患者左右、上下、前后方向平移及旋转误差,分析摆位误差及CTV外放边界。采用配对t检验差异。结果 CBCT校正前后均为304次,治疗后68次。所有患者分次间左右、上下、前后方向平移误差和旋转误差经在线校正后均减小,校正前/后绝对值的平均值分别为2.42 mm/0.42 mm、3.55 mm/0.47 mm、3.26 mm/0.27 mm和1.24°/0.24°、0.70°/0.32°、0.57°/0.12°(P=0.036、0.000、0.000、0.002、0.000、0.004)。考虑分次内摆位误差影响,治疗床校正后CTV外扩边界在左右、上下、前后方向上分别为2.24、3.32、2.20 mm。结论 宫颈癌术后患者CBCT联合六维治疗床在线校正可明显减小6个方向分次间摆位误差,且能缩小CTV外放边界。

Analysis of setup errors and planning target margin by cone-beam CT in combination with HexaPOD evo RT 6D couch for postoperative patients of cervical cancer

Objective To evaluate the setup errors and CTV margins by kV cone-beam CT in combination with HexaPOD evo RT 6D treatment couch for postoperative patients with cervical cancer. Methods Between July 2013 and March 2014,17 postoperative patients with cervical cancer were prospectively enrolled in the study. Each patient would scan the first CBCT after conventional positioning,and their scan after 6D couch online correction,and the last scan after delivery. Then the scans were registered to the planning CT to determine the inter-and intrafractional setup errors in translational and rotational directions. PTV margins were calculated from the systematic (∑) and random (σ) errors. Results Data set for a total of 676 CBCT scans were obtained from the 17 patients, in which before and after the 6D couch correction were both 304 and after delivery was 68.The interfractional setup errors in translational and rotational directions by 6D couch online correction were significantly decreased. The average absolute values of the pre-/post-correction errors were 2.42 mm/0.42 mm x-axis,3.55 mm/0.47 mm y-axis,3.26 mm/0.27 mm z-axis,1.24°/0.24°pitch,0.70°/0.32°roll,0.57°/0.12°yaw, respectively (P=0.036,0.000,0.000,0.002,0.000,0.004). The total PTV margins (M_PTV) accounting for 6D couch online correction and intrafraction errors were 2.24,3.32,2.20 mm in the left-right (x-axis),superior-inferior (y-axis) and anterior-posterior (z-axis) directions, respectively. Conclusions CBCT in combination with HexaPOD evo RT 6D is an effective modality to evaluate and improve the accuracy of IMRT in postoperative patients with cervical cancer,while putting narrow target margin to reduce the irradiation of normal tissues.