直线加速器机载千伏级扇形束CT和兆伏级锥形束CT系统在放疗摆位误差中的应用

Application of Linear Accelerator on Boarding Kilovolt Fan Beam CT and Megavolt Cone Beam CT System on Set-up Errors During Radiation Treatment

目的应用直线加速器机载千伏级扇形束CT(kV-FBCT)及兆伏级锥形束CT(MV-CBCT)定量分析不同治疗部位的肿瘤患者调强放射治疗期间的摆位误差,为制定临床靶区外放边界提供参考。方法回顾性分析我科行放射治疗的患者,分别于每次常规摆位后,调强放射治疗前行kV-FBCT和(或)MV-CBCT扫描,与计划CT配准,纠正摆位,获取每次摆位误差,根据患者的位移计算不同治疗部位患者在左右、前后、头脚方向上的平均位移M、系统误差(Σ)和随机误差(б),通过PTV边界公式(2.5Σ+0.7б)估计在该方向所需要的外放边界。根据同一个患者的单次放疗获得三维位移。结果70例患者共记录到1130人次位移偏差,根据外扩边界公式得出三个方向上所需的PTV边界。头颈1.9~3.1 mm,胸部2.8~5.1 mm,乳腺4.6~5.1 mm,上腹部3.0~5.5 mm及盆腔3.5~6.8 mm。3D平均位移头颈、胸部、乳腺、上腹部和盆腔分别为2.4±1.0 mm、4.0±1.6 mm、4.1±2.0 mm、4.6±2.1 mm及4.6±2.1 mm。利用kV-FBCT和MV-CBCT校位所得3D位移中位值分别为:4.1 mm和3.4 mm,差异无统计学意义(P=0.212)。结论直线加速器机载FBCT均可获得相似的可定量的摆位误差数据,但非等中心的影像引导所致的潜在误差不能忽略。

Objective To quantify the setup errors for the different anatomical sites of patients who received intensity-modulated radiotherapy(IMRT)with linear accelerator on-board kilovolt fan beam CT(kV-FBCT)as non-isocenter IGRT and megavolt cone beam CT(MV-CBCT)as isocenter IGRT.Methods A retrospective analysis was performedon 70 patients who underwent radiotherapy,kV-FBCT,and/or MV-CBCT scans after each routine setup prior to IMRT.The average displacement(M),systematic error(Σ),and random error(б)at different treatment sites in the left-right,anterior-posterior,and cranialcaudal directions were calculated according to the individual displacements.The formula 2.5Σ+0.7бwas used to estimate the PTV margin in respective direction.For each single patient,the root mean square in three directions was used as 3D displacement.Results A total of 1130 displacements were recorded in the 70 patients.The PTV margin was estimated to be 1.9-3.1 mm in head and neck cancer,2.8-5.1 mm in thoracic cancer,4.6-5.1 mm in breast cancer,3.0-5.5 mm in upper abdominal cancer,and 3.5-6.8 mm in pelvic tumor.For the 3D mean displacements,the head and neck,thoracic,breast,upper abdominal,and pelvic cancer were 2.4±1.0,4.0±1.6,4.1±2.0,4.6±2.1,and 4.6±2.1 mm,respectively.The average 3D displacement obtained by kV-FBCT and MV-CBCT were 4.1 and 3.4 mm,respectively(P=0.212).Conclusion The quantitative setup-error data can be obtained using linear accelerator on-board FBCT,and the non-isocenter IGRT induced set-up error cannot be negligible.