基于XVI行容积旋转调强放疗治疗盆腔肿瘤摆位误差分析

摘要

Objective To acquire setup error with X-ray volumetric images (XVI) technique during volumetric modulated arc therapy (VMAT) of pelvic tumors in order to provide guidance for the doctor to determine the interval between clinical target volume (CTV) and planning target volume (PTV).~ Totally 20 pelvic tumor patients accepting radiation oncology underwent CBCT scan before the first treatment,and auto registration was executed between CBCT images and planning CT images to determine the setup errors at X,Y and Z directions.Then the patients experienced another CBCT scan to obtain residual setup errors,VMAT was carried out after auto on-line correction by the treatment couch,and the third CBCT scan was performed after the treatment.Totally three times of CBCT scans were implemented every week hereafter.The setup errors were analyzed before and after the treatment,and the target volume margin (MPTV) was calculated accordingly.Results The setup errors at X,Y and Z directions were significantly decreased after correction.The values of MPTV at X,Y and Z directions before correction were 3.89,6.20 and 5.24 mm respectively,and the ones after correction were 1.42,2.42 and 2.40 mm respectively.The decreased values of MPTV were between 2.47 and 3.78 mm,which showed the most significant trend at Y direction.Conclusion VMAT of pelvic tumors based on XVI contributes to decreasing the setup errors and enhancing treatment quality.%目的:研究容积旋转调强放疗(volumetric modulated arc therapy,VMAT)治疗盆腔肿瘤时利用X线容积图像(X-ray volumetric images,XVI)获得的患者摆位误差,为医生勾画临床靶区(clinical target volume,CTV)与计划靶区(planning target volume,PTV)之间的间距大小提供依据.方法:选择20例盆腔肿瘤放疗的患者,每位患者首次治疗前行锥形柬CT(cone beam CT,CBCT)扫描,将CBCT图像和计划CT图像进行自动配准,计算出患者三维方向的摆位误差;再次行CBCT扫描得出剩余摆位误差,经治疗床自动在线校正后行VMAT治疗,治疗结束后进行第3次扫描.以后每周行3次CBCT扫描.分析治疗前后系统的摆位误差,并根据摆位误差计算靶区外放值(MPIV).结果:CBCT校正后X、Y、Z轴的摆位误差有效降低.校正前X、Y、Z轴肘MPIV分别为3.89、6.20、5.24 mm,校正后分别为1.42、2.42、2.40 mm.校正后MPTV的减少幅度为2.47～3.78 mm,以y轴最明显.结论:基于XVI行VMAT治疗盆腔肿瘤可降低患者的摆位误差,提高摆位精度,保证治疗质量.