鼻咽癌调强放疗中的CTV-PTV边界大小分析

The Study of CTV-PTV Margin During the Treatment of Nasopharyngeal Carcinoma with Intensity Modulation Radiation Therapy

目的探讨采用射野验证片测量的鼻咽癌调强放疗(IMRT)摆位误差的方法,并分析CTV的外扩范围大小。方法 10例行三维适行放疗的鼻咽癌患者,均用面罩固定,放疗过程中每周拍射野验证片,通过比较DRR和验证片上骨性标志与射野的相对位置来计算摆位误差。根据摆位误差计算CTV到PTV应预留边界的大小。结果 10例患者共摄取120张射野验证片,有11张射野片因为无法辨认出两个或两个以上解剖结构而被剔除。将各方向的随机和系统误差分别计算。左右、头脚、前后各向总误差为2.8、2.7、2.8mm,系统误差分别为2.4、2.3、2.4mm,随机误差分别为1.4、1.5、1.5mm,移动均值分别为-1.1、-0.1、-0.25mm。三维方向上摆位偏移大于3mm26.3%,大于4mm15.1%,大于5mm6.5%。单一方向上平均摆位偏移大于3mm:左右17.5%、头脚20.0%、前后22.5%。CTV与PTV间预留间隙6mm可行。结论在鼻咽癌的IMRT中,用本课题的固定及摆位技术,CTV与PTV间预留间隙6mm是可行的。

Objective To investigate the positioning errors in the treatment of nasopharyngeal carcinoma with intensity modulation radiation therapy（IMRT） by portal film and defined margins for the definition of planning target volume.Methods The positioning data of 10 patients treated with IMRT for nasopharyngeal carcinoma were analyzed.Orthogonal verification films were taken once one week.Field shape and an anatomy template consisting of contours of relevant bony structures on DRR and portal film swerve drawn and compared to obtain the positioning data,and random and systematic positioning deviations were measured.Margins for CTV-PTV were defined accounting to systematic and random positioning uncertainties.Results One hundred and twenty images were obtained from the treatment of the 10 patients.Eleven images were excluded due to poor quality that it could not used to identify two or more relevant bony structures.For each patient,the systematic and random errors for the different directions were measured respectively.The over all positioning errors showed 2.4 mm,2.3 mm,2.4 mm along the left-right,craniocaudal and anterior-posterior directions,respectively.The systematic component was 2.4 mm,2.3 mm,2.4 mm and the random positioning component was 1.4 mm,1.5 mm,1.5 mm in the left-right,craniocaudal and ventrodorsal directions,respectively.The overall mean deviation was -1.1 mm,-0.1 mm,-0.25 mm in the left-right,craniocaudal and ventrodorsal directions,respectively.26.3% of positioning with three dimensional positioning deviations greater than 3 mm but less than 4 mm,15.1% greater than 4 mm but less than 5 mm,6.5% with 5 mm or more.Unilateral positioning deviation with more than 3 mm was 17.5%,20.0% and 22.5%,in the left-right,craniocaudal and ventrodorsal directions,respectively.The 6 mm of CTV-PTV margins were feasible in all three directions.Conclusion The application of proposed recipes for CTV-PTV margins indicates that 6 mm is feasible in nasopharyngeal carcinoma radiotherapy with the immobilizing and positioning technique in our hospital.