基于螺旋断层放疗系统的1458次兆伏级 CT图像分析各部位肿瘤治疗摆位误差

A quantitative analysis of tumor site specific setup based on 1 485 daily MVCT scans from helical tomotherapy

目的：通过螺旋断层放疗系统的兆伏级 CT（MVCT）图像引导技术，定量分析三种不同部位肿瘤治疗的摆位误差，为各部位临床靶区外扩范围提供合理的边界值，提高临床精确放疗效果。方法选取进行螺旋断层放疗的肿瘤患者60例，均通过 MVCT 扫描图像引导摆位，分别对587次头颈部、500次胸部、371次腹腔及盆腔肿瘤 MVCT 图像校正的平移和旋转误差进行统计，计算各部位肿瘤误差发生率，通过GraphPad Prism 5制作三维误差分布直方图，同时分析摆位系统误差和随机误差，并通过经验公式分析靶区最佳外扩值。结果60例患者共经 MVCT 扫描1458次。头颈部肿瘤在三维方向误差发生率远低于胸部和腹腔及盆腔肿瘤，摆位误差值≥3 mm 时，头颈、胸部、腹腔及盆腔误差发生率分别为55．3％、70．8％、79．8％，误差值≥5 mm 时，三者分别为17．5％、40．6％、47．2％。对于旋转误差，头颈部发生率略高于其他部位。各部位的系统误差在－1．4～2．7 mm 之间，腹腔及妇科部位在治疗床升降方向的误差分布大于其他部位（χ2＝19．3， P ＜0．05），系统误差值为2．7 mm。头颈、胸部、腹腔及盆腔肿瘤需分别在 CTV 基础上外扩4～7、9～14、10～17 mm。结论头颈部、胸部、腹腔及盆腔肿瘤患者治疗摆位时在三维方向误差分布各有差异，每天放疗前的MVCT 图像引导可显著降低摆位误差的发生率，也为确定靶区外扩范围提供依据，从而实施精确放疗提高患者治愈率。

Objective To assess the variation in patient setup corrections for three different anatomic treat-ment sites using daily pretreatment megavoltage CT（MVCT）in helical tomotherapy,and to analyze alternative refer-ence margins for specific tumor site.Methods Sixty patients treated for three anatomical sites on helical tomotherapy were analyzed.Daily MVCT was carried out for registration and setup corrections before each treatment fraction.Setup errors and rotational setup corrections from 587 head and neck,500 thoracic,371 abdomen and gynecology MCVT imaging were input to statistical analysis.Incidences of three dimensional vector error lengths were calculated for each anatomic site.Overall distribution histograms of the three -dimensionally error was presented using GraphPad Prism 5.The distributions of systematic and random setup errors were quantitative analyzed and the additional margins required were also taken into account.Results 1 458 MVCT scans were implemented for sixty patients.Head and neck had lower frequencies of translational setup errors than others.Frequency of at least 3mm three -dimensional setup errors for head and neck,thoracic,abdomen and gynecology was 55.3%,70.8%,79.8%,respectively.This fre-quency decreased to 17.5%,40.6%,47.2% if 3D vector distance ≥5mm was scored.Overall systematic errors ranged from -1.4mm to 2.7mm,abdomen and gynecology had the largest setup errors in the vertical direction which was statistically significant（χ2 =19.3,P 〈0.05）.The suggested margins should be increased by 4 -7 mm in three -dimensional direction for head and neck,9 -14mm for thoracic,10 -17mm for abdomen and gynecology.Conclusion Differences in setup corrections are perceived between head and neck,thoracic,abdomen and gynecology.The accura-cy of patient positioning can be improved if pre -treatment daily MVCT scans are put into use.Results from setup cor-rection can provide evidence for tumor treatment margin and improve the accuracy of regular radiotherapy.