头颈部肿瘤放疗颈直位与过伸位两种固定方法摆位误差分析

Analysis of Position Errors Between Two Fixed Methods of Straight Neck Position and Neck Hyperextension Position in Head and Neck Cancer Radiotherapies

目的通过比较两种不同的摆位固定方法,探讨不同固定方法在提高放疗精确性上的差异。方法所有患者均采用平躺仰卧位、头颈肩热塑膜加真空袋固定,采用相同的头颈肩调强定位治疗板和三维适形及调强放疗(Intensity Modulated Radiation Therapy,IMRT)进行治疗。对照组患者采用颈直位,研究组患者采用过伸位。根据电子射野影像系统(Electronic Portal Imaging Device,EPID)图像与数字重建射线影像(Digitally Reconstructed Radiograph,DRR)在系统中配准获得各个方向的偏差,从而计算出各自的摆位误差和外放边界。结果对照组和研究组在左右、头脚、腹背方向上的摆位误差分别为(0.09±0.07)、(0.23±0.19)、(0.19±0.21)mm和(0.06±0.08)、(0.15±0.12)、(0.12±0.12)mm;对照组和研究组的外放边界分别为0.26、0.49、0.50 mm和0.24、0.33、0.40 mm。两组患者在3个方向摆位线性误差比较P分别为0.075、0.032、0.047。结论其它固定条件相同时,过伸位的固定效果优于颈直位;研究组的外放边界较对照组小,说明采用过伸位时放疗部位相对更精确。建议在患者配合程度好、时间充裕的情况下首选过伸位的固定方法。

Objective To explore the difference between two different fixation methods in improving the accuracy of radiotherapy. Methods All the patients were treated with supine position, fixation of patient＇s head, neck and shoulder with thermoplastic films and vacuum bags, the same head, neck and shoulder intensity positioning treatment plate, three-dimensional conformal radiotherapy and IMRT（Intensity Modulated Radiation Therapy）. Patients in Control Group were treated in straight neck position; while, patients in Study Group were treated in neck hyperextension position. Deviations in every direction was acquired through registration of EPID（Electronic Portal Imaging System） and DRR（Digitally Reconstructed Radiograph） to calculate the setup errors and outer margins respectively. Results Setup errors in the left and right, head and feet, dorsal and ventral direction of Control Group and Study Group were（0.09±0.07）,（0.23±0.19）,（0.19±0.21） mm and（0.06±0.08）,（0.15±0.12）,（0.12±0.12） mm respectively; the outer margins of Control Group and Study Group were 0.26, 0.49, 0.50 mm and 0.24, 0.33, 0.40 mm respectively. The linear errors of two groups in the 3 directions were 0.075, 0.032, 0.047 respectively. Conclusion When other conditions were the same, the fixation effect of neck hyperextension position was superior than that of straight neck position; the outer margin of Study Group was smaller than that of Control Group, indicated that adoption of the neck hyperextension position as the radiotherapy location was relatively more precise. And it was recommended to adopt the neck hyperextension position fixation method for patients with a good degree of coordination in case of abundant time.