6D治疗床联合锥形束CT引导下妇科肿瘤摆位误差及计划靶区外放边界研究

目的 探究6D治疗床联合锥形束CT(CBCT)容积旋转调强(VMAT)治疗妇科肿瘤患者的摆位误差,以及其靶区外放边界的变化趋势。方法 妇科肿瘤术后患者20例,采用HexaPOD^TMevo RT 6D治疗床和kV级CBCT影像引导的容积调强放射治疗。所有患者常规摆位后均行校正前CBCT扫描,利用6D治疗床在线校正后,再次行CBCT扫描,治疗后第3次行CBCT扫描,分别获得校正前、校正后、治疗后X射线容积影像,所有容积图像与计划CT图像采用自动骨性标记和手动微调的配准方式,获得三维平移(x、y、z)和旋转方向(Rx、Ry、Rz)的摆位误差,分析其摆位误差及计划靶区外放边界。结果 患者共行CBCT扫描594次,6D治疗床在线校正后,分次间摆位误差在y、z、Rx、Ry、Rz轴方向上明显缩小(t=6.21、-8.60、2.13、-8.51、-3.48,P<0.05)。外扩边界M_PTV在x轴、y轴、z轴方向上分别为2.20、3.43、2.00 mm,校正前后减少幅度为4.46~6.05 mm。结论 6D治疗床联合CBCT可明显提高妇科肿瘤盆腔放疗患者的摆位精度,同时可为精确设定计划靶区外放边界提供可靠依据。

Setup errors and planning target margin by 6D radiotherapy couch combined with cone-beam CT during volumetric modulated arc therapy in gynecological cancer patients

Objective To evaluate inter-and intrafractional setup errors by 6-degree-of-freedom(6D)treatment couch in combination with kV cone-beam CT for gynecological cancer patients, and calculate planning target volume(PTV)margins.Methods Twenty postoperative gynecological cancer patients, who were scheduled to undergo volumetric modulated arc therapy(VMAT), were prospectively enrolled in the study. 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 6D couch online correction. After VMAT delivery, a final CBCT was acquired to assess intra-fraction motion. The PTV margins were calculated from the above setup variations.Results A total of 594 CBCT images were acquired from 20 patients. After the 6D couch online correction, the interfractional setup errors in y,z,Rx,Ry,Rz axis were significantly reduced(t=6.21,-8.60,2.13,-8.51,-3.48,P<0.05). The total PTV margins(M_PTV)accounting for 6D couch online correction and intrafraction errors were 2.20, 3.43, 2.00 mm in the left-right(x axis), superior-inferior(y axis)and anterior-posterior(z axis)directions, respectively. After the 6D couch online correction, the reduction of M_PTV ranged from 4.46 to 6.05 mm.Conclusions 6D in combination with CBCT could effectively improve the setup error accuracy of VMAT in postoperative gynecological cancer patients, while providing reliable basis for delineating the M_PTV.