量化分析R624-SCF型固定装置在肺部SBRT过程中摆位误差

摘要

目的 应用KV-CBCT评估R624-SCF型固定装置在肺部SBRT治疗过程中的摆位误差,定量分析放疗过程中各种误差在累计摆位误差中的占比情况,揭示摆位误差的主要来源.方法 采集32例肺部肿瘤患者每周的CBCT数据及加速器每个月的QA数据,定量计算不同摆位误差.使用统计模型计算累计误差,并分析各次误差占比情况及来源.结果 32例患者通过420次CBCT扫描.固定装置的摆位在水平、头脚、垂直3个方向上的误差分别为(0.03±0.72)、(0.73±1.16)、(-0.21±0.95)mm.肿瘤靶区运动位移在水平、头脚、垂直3个方向上的误差分别为(0.71±2.61)、(-0.80±2.60)、(0.075±1.77) mm.通过Vance Keeling公式计算误差,得到线性模型中各项误差占比情况:累计误差54.55％,固定装置9.21％,肿瘤运动12.97％,治疗床沉降2.55％,机架旋转中心5.70％,准直器旋转中心4.73％,治疗床旋转中心4.61％,X线射野中心5.70％.结论 肺癌SBRT治疗过程中造成靶区误差的主要因素依次为摆位的随机性、肿瘤运动、固定装置、治疗床沉降以及机器等中心.在放疗过程中有针对性地控制肿瘤运动,对减小累计误差有重要意义.%Objective KV-CBCT was utilized to evaluate the setup errors in lung SBRT with R624-SCF immobilization equipment,quantitatively analyze the percentage of all types of errors in the cumulative errors and unravel the main sources of setup errors.Methods The CBCT data weekly and QA data monthly from 32 patients diagnosed with lung neoplasms were collected to quantitatively analyze the setup errors.The cumulative errors were calculated by statistical model.The proportion and source of each type of setup error was analyzed.Results All 32 patients received a total of 420 times of CBCT.The setup errors of immobilization equipment in the lateral,supine-inferior,anterior-posterior directions were (0.03±0.72) mm,(0.73± 1.16) mm and (0.21±0.95) mm,respectively.The errors of tumor motion in three directions were (0.71±2.61) mm,(-0.80±2.60) mm and (0.075± 1.77) mm,respectively.According to the calculation formula proposed by Vance Keeling,the proportion of the cumulative error was 54.55％,9.21％ for immobilization equipment,12.97％ for tumor motion,2.55％ for couch sagging,5.70％ for Gantry radiation isocenter,4.73％ for Collimator radiation isocenter,4.61％ for couch radiation isocenter and 5.70％ for Xray field isocenter,respectively.Conclusions The main factors of setup errors during SBRT treatment for lung cancer are setup random,tumor motion,immobilization equipment,couch sagging and machine isocenter.During radiotherapy,targeted control of tumor motion is of significance for minimizing the cumulative errors.