应用IGRT机载KV-CBCT校正胸腹部肿瘤调强适形放疗摆位误差的研究

Measurement and Analysis of Set-up Errors with the Use of CBCT in IMRT and 3DCRT of the Thoracic and Abdominal Tumors

目的应用IGRT机载KV-CBCT校正胸腹部肿瘤调强适形放疗摆位误差,分析校正前后摆位误差的变化。方法应用医科达SynergyIGRT加速器机载千伏级锥形束CT(KV-CBCT)扫描,采集的X线容积图像(XVI)与计划CT图像的靶中心匹配,获得患者X(左右)、Y(头脚)、Z(前后)3个方向的线性误差和旋转误差,并对误差进行校正。对28例胸腹部肿瘤调强适形放疗患者每次治疗时,分别于校正前后各扫描一次CBCT,共校正334次,获得668组XVI数据,分析校正前后摆位误差的变化情况。结果测量得出系统误差±随机误差在校正前X、Y、Z方向上,线性误差分别为(0.94±1.25)mm、(-1.77±3.27)mm、(-0.57±1.28)mm,旋转误差分别为(0.74±0.59)°、(0.09±0.94)°、(-0.22±0.63)°;校正后线性误差分别为(-0.01±0.41)mm、(-0.13±0.56)mm、(-0.24±0.40)mm,旋转误差分别为(0.13±0.38)°、(-0.07±0.51)°、(-0.04±0.36)°,校正后的系统误差和随机误差均低于校正前。根据vanHerk等的摆位扩边公式MPTV=2.5Σ+0.7δ,计算得出X、Y、Z方向的MPTV值,校正后较校正前分别减少2.81mm、7.18mm、4.79mm。结论通过CBCT对放疗摆位中出现的线性误差和旋转误差进行校正,可以大大缩小系统误差和随机误差,从而缩小CTV—PTV的摆位扩边,提高放疗的精确性。

Objective This study is to analyze the change of the set-up errors between after the initial setup and auto-repositienning with the use of CBCT in IMRT and 3DCRT of the Thoracic and Abdominal Tumors.Methods Twenty-eight patients with thoracic or abdominal cancer and treated with IMRT or 3DCRT were included in this study.With the CBCT on the Elekta Synergy Linear Accelerator,we scaned the patients after the initial setup and auto-repositienning and acquired XVI(X-Ray volume Image) to match with the TPS Images.668 groups of translational and rotational errors in the x(left-right),y (anterior-posterior) and z (superior-inferior) axis from 334 adjustments were analysed.Results The translational errors after the initial setup were (0.94±1.25)mm,(-1.77±3.27)mm and (-0.57±1.28)mm,rotational errors were (0.74±0.59)°,(0.09±0.94)°and (-0.22±0.63)°.The translational errors after auto-repositienning were (-0.01±0.41)mm,(-0.13±0.56)mm and(-0.24±0.40)mm,and the rotation errors were (0.13±0.38)°,(-0.07±0.51)°and (-0.04±0.36)°.Both the systematic errors and random errors after auto-repositienning were smaller than the errors after the initial setup.According to the Van Herk formula MPTV=2.5Σ+0.7δ,the margins in x,y and z axis after auto-repositienning were reduced to 2.81 mm,7.18 mm and 4.79 mm.Conclusion The systematic errors and random errors can be reduced obviously with the use of CBCT.Therefore,the margins from CTV-PTV could be reduced,so as to improve the treatment accuracy.