放疗定位膜制作及体位固定质量控制

Quality control of positioning membrane production and posture fixation in radiotherapy

目的：通过放疗定位膜制作及放疗摆位实践,分析影响放疗体位固定及定位膜制作的各种因素,探讨不同部位肿瘤放疗时最佳体位固定方法及定位膜制作流程中的注意事项,提高放疗摆位精确性。方法：选取2013年6月~2014年1月间,在瓦里安True Beam1103直线加速器治疗的头颈部患者37例;在瓦里安Rapid Arc直线加速器治疗的胸部患者56例,盆腔患者43例。所有患者在首次放疗前行KV-CBCT扫描,以后每周扫描1次。应用Offline Review软件,将CBCT扫描图像和计划CT图像进行配准,分析靶中心在x轴（左右）、y轴（背腹）、z轴（头脚）方向上的误差值及其误差分布情况。结果：系统误差（均数）±随机误差（标准差）在左右（x）方向、背腹（y）方向、头脚（z）方向分别为头颈部x（0.98±0.79）mm,y（0.96±0.86）mm,z（1.13±0.99）mm;胸部x（2.11±1.56）mm,y（1.52±1.22）mm,z（2.50±1.68）mm;盆腔x（1.89±1.43）mm,y（1.33±1.25）mm,z（2.48±1.62）mm。在放疗过程中,头颈部患者摆位平均偏差小于2 mm,胸部及盆腔患者摆位平均偏差均小于3 mm,完全达到了调强放射治疗摆位精度的要求。结论：放疗定位膜体位固定技术是开展调强放疗的重要环节,放射治疗技师通过对不同部位热塑定位膜制作和体位固定技术的合理应用,可以明显提高患者体位的重复性和准确性,从而减少放疗摆位误差,对调强放疗肿瘤靶区剂量的准确实施很有意义。

Objective Based on the thermoplastic positioning membrane production and positioning practice in radiotherapy, to improve the positioning accuracy in the radiotherapy by analyzing the factors influencing position fixation and thermoplastic positioning membrane production, and discussing on the best way for posture fixation in the radiotherapy for tumors in different body regions and the considerations in positioning membrane production. Methods From June 2013 to January 2014, 37 patients with head and neck tumor treated by Varian TrueBeam 1103 linear accelerator, and 99 patients treated by the Varian RapidArc linear accelerator, including 56 patients with thoracic tumor and 43 patients with pelvic tumor, were selected. All patients were scanned by kilovoltage cone-beam computer tomography （kV-CBCT） before the first radiotherapy. Afterward patients were scanned once a week. The Offline Review software was applied to register the acquired CBCT images with planning CT images. And the positioning errors and error distributions of iso-center positions on the axes of x （left-fight）, y （belly-back） and z （head-foot） were analyzed. Results The systemic error （average） ± random errors （standard deviation） in the x, y and Z directions were respectively （0.98±0.79） mm, （0.96±0.86） mm, （1.13±0.99） mm for the head and neck tumor; （2.11 ± 1.56） mm, （1.52±1.22） mm, （2.50±1.68） mm for the thoracic tumor; （1.89＋1.43） mm, （1.33±1.25） mm, （2.48±1.62） mm for the pelvic tumor. The average positioning error of patients with head and neck tumor was less than 2 mm while that of patients with thoracic tumor and pelvic tumor was less than 3 mm, fully meeting the requirement of positioning accuracy in intensity modulated radiotherapy （IMRT）. Conclusion The positioning membrane and position fixation technique play important roles in IMRT. The radiation therapy technologist can improve the repeatability and accuracy of patient positioning by the proper thermoplastic positioning membrane production and positioning fixation for tumors in different regions, reducing the positioning errors in IMRT, which has significant meanings for implementing accurate dose to target volumes in IMRT.