应用锥形束CT评估鼻咽癌调强放疗中的摆位误差

目的探讨锥形束CT(cone-beam computed tomography,CBCT)扫描在调强放射治疗鼻咽癌中降低摆位误差的方法。方法对调强放疗的15例鼻咽癌患者,使用瓦里安23EX直线加速器的机载影像系统(on-bo-rad-imager),采集首次摆位后、摆位误差纠正后及治疗后CBCT图像,并与计划系统的模拟定位CT图像靶中心匹配计划,获得首次摆位后、摆位误差纠正后及治疗后在X(左右)、Y(腹背)、Z(头脚)方向摆位误差进行分析。每位患者每周1次,每次采集3组数据,15例患者治疗5～7w。结果 15例鼻咽癌患者CBCT扫描首次摆位误差数据在X、Y、Z轴分别为(0.675±2.023)、(0.337±1.508)、(0.450±1.749)mm;3个轴向摆位误差绝对值的P95分别为4、3、4mm;3轴向的众数分别为1、1、0mm;其中X轴方向91.3%≤3mm,Y轴方向100%≤3mm,Z轴方向92.5%≤3mm。X、Y、Z轴上极小值分别为-6.00、-3.00、-5.00mm,极大值分别为5.00、3.00、5.00mm。分次治疗间摆位误差差异有统计学意义(P<0.05),分次治疗内摆位误差及X、Y、Z三维方向上的摆位误差差异无统计学意义(P>0.05)。结论采用CBCT技术对鼻咽癌调强放疗进行摆位纠正,可以缩小鼻咽癌放疗过程中分次间的摆位误差,而分次治疗内误差较小,放疗中只需要在首次摆位后治疗前进行CBCT摆位纠正。

Evaluate of setup error in head and neck tumors with intensity modulated radiation therapy by cone-beam computed tomography

Objective To analyze the inter and ental fractionation setup error in head and neck tumors with intensity modulated radiation therapy(IMRT) by cone-beam computed tomography(CBCT),to approach the method for reducing setup error.Methods Fifty patients with head and neck tumor were collected CBCT images after initial setup,after re-positioning and after radiation by On-Borad-Imager of Varian 23EX linear accelerator,and to match the positioning CT images before radiation therapy through target center in planning system,then analyzed setup errors after initial setup,after re-positioning and after radiation in X(left-right),Y(cranial-caudal) and Z(ventral-dorsal) directions.CBCT images were collected 3 times per week for every patients and the therapy to last 5~7 weeks.Results 15 patients received a total of 240 CBCT scans.After analyzed the data of initial setup error,the systematic±random errors in X,Y,and Z directions were(0.675 0±2.023 8),(0.337 5±1.508 9),(0.450 0±1.749 5) mm,respectively.The P95 of setup error absolute value in three directions were 4,3 and 4 mm;and the mode in three directions were 1,1 and 0 mm;X direction 91.3% ≤3 mm,Y direction 100%≤3 mm,Z direction 92.5%≤3 mm.The minimal value of X,Y and Z directions was 6,3 and 5 mm.Setup error of dividing treatment was statistically significant(P<0.05),fractionated treatment setup errors and the X,Y,Z three dimensions positioning error of the difference was not statistically significant(P>0.05) between fractionated treatment.Conclusion Setup rectification in head and neck tumor patients with IMRT by CBCT scan can reduce the inter fractionation setup error,and the ental fractionation setup error was smaller,so we need retrieve initial setup error only in radiotherapy.