锥形束CT离线校正肺癌摆位误差

Off-line correction for cone-beam CT setup errors of lung cancer

目的:应用锥形束CT(CBCT)测量肺癌患者的摆位误差,探讨摆位误差离线校正方法。方法:选取21例胸部肿瘤患者,分次放疗前每日行CBCT扫描1次,通过与计划CT配准后,记录患者左右、前后及头脚方向的摆位误差,并计算出PTV的扩边大小。模拟两种摆位误差离线校正策略,分别通过首次治疗时图像引导(M1)和前3次治疗图像引导(M2)的摆位误差校正治疗床的位置,根据等中心的激光线在体模上重新标记等中心位置。分析采用不同策略校正后的摆位误差。结果:无图像引导时,本中心肺部肿瘤的摆位误差在左右、前后与头脚方向的摆位误差分别为(-0.40±1.91)、(-0.71±0.38)、(-1.37±0.94)mm;与之相对应的计划靶区(PTV)扩边分别为5.49、4.31、8.96 mm。使用两种离线校正后,左右、前后与头脚方向的摆位误差分别为(0.13±1.91)、(-0.57±0.38)、(1.06±0.94)mm(M1),(0.05±1.91)、(-0.11±0.38)、(0.52±0.94)mm(M2);对应的PTV扩边缩小为4.82、4.11、7.60 mm(M1),4.04、1.60、3.28 mm(M2)。结论:离线校正能减小摆位误差,缩小PTV扩边,保证治疗质量的同时提高临床效率。

Abstract： Objective To measure the setup errors of patients with lung cancer by using cone-beam CT （CBCT） and to study on the off-line correction for CBCT setup errors of lung cancer. Methods Totally, 21 patients with lung cancer were selectde. Before radiotherapy, each patient accepted a CBCT scan each day. After the registration with the planning CT, the setup errors from three directions, left-right （LR）, anterior-posterior （AP）, superior-interior （SI） were recorded and the planning target volume （PTV） margin was calculated. Two kinds of off-line correction strategies for CBCT setup errors were simulated, correcting the position of treatment couch by the setup errors of image guidance in the first treatment （MI） and image guidance in the first three treatments （M2）, and resetting the treatment isocenter markers on the thermoplastic mask according to the isocenter laser. The setup errors after the corrections of different strategies were analyzed. Results Without image-guidance, the setup errors of patients with lung cancer in the directions of LR, AP and SI were respectively （-0.40±1.91） mm, （-0.71±0.38） mm, （-1.37±0.94） mm, and the corresponding PTV margins were respectively 5.49 mm, 4.31 mm, 8.96 mm. With two kinds of off-line corrections, the setup errors of M 1 in the directions of LR, AP and SI were respectively （0.13± 1.91） mm, （-0.57±0.38） mm, （1.06±0.94） mm, and those of M2 were respectively （0.05±1.91） mm, （-0.11±0.38） mm, （0.52±0.94） mm. The ccorresponding PTV margins of M 1 were respectively 4.82 mm, 4.11mm, 7.60 mm, and those of M2 were respectively 4.04 mm, 1.60 mm, 3.28 mm. Conclusion The off-line correction reduces the setup error and PTV margin, improves the treatment efficiency without affecting the treatment quality.