CBCT引导下不同体位子宫肿瘤IMRT摆位误差及其外放边界

Setup errors and margins of CBCT-guided IMRT in different positions for uterine neoplasms

目的:研究在千伏级CBCT引导下,不同体位子宫肿瘤患者调强放射治疗中的摆位误差及靶区的外放边界。方法:采用医科达直线加速器机载影像系统对251例子宫肿瘤患者接受调强放射治疗前行CBCT扫描,其中仰卧位117例、俯卧位134例。系统自动重建图像并与治疗计划CT图像进行配准,获得俯卧位与仰卧位患者x、y、z方向摆位误差,并分别计算患者临床靶区到计划靶区(PTV)的外放边界。结果:所有患者共行3 128次扫描,俯卧位1 679次与仰卧位1 449次。x、y、z轴的误差均小于0.3 cm为981次,占31.36%;距离治疗等中心偏差距离小于0.3 cm为415次,占13.27%。考虑摆位误差方向时,俯卧位患者的x、y、z方向上摆位误差分别为(0.109 5±0.380 7)、(-0.035 1±0.569 2)、(0.075 1±0.285 2)cm;仰卧位患者的x、y、z方向上摆位误差分别为(0.001 1±0.303 4)、(0.118 4±0.583 0)、(0.033 2±0.248 0)cm。而考虑摆位误差大小时,俯卧位患者的x、y、z方向上摆位误差分别(0.300 8±0.257 7)、(0.442 8±0.359 2)、(0.227 1±0.188 2)cm;仰卧位患者的x、y、z方向上摆位误差分别为(0.229 3±0.198 6)、(0.470 2±0.364 4)、(0.183 2±0.170 3)cm。俯卧位患者PTV在x、y、z方向分别外放0.540、0.486、0.387 cm;仰卧位患者PTV在x、y、z方向分别外放0.215、0.704、0.257 cm。结论:子宫肿瘤患者仰卧位和俯卧位这两种体位的摆位误差有一定差异,以距离治疗等中心偏差距离小于0.3 cm作为摆位误差校准较适合;俯卧位患者的靶区在x、y、z方向分别外放0.540、0.486、0.387 cm;而仰卧位患者则外放0.215、0.704、0.257 cm。

Objective To study the setup errors and margins in intensity-modulated radiotherapy guided by kV-cone-beam computed tomography(CBCT)for patients with uterine neoplasms who were in prone or supine position.Methods Before radiotherapy began,Elekta Synergy with on-board imager was used to perform CBCT scans on 251 patients with uterine neoplasms,including 117 patients in supine position and 134 in prone position.The setup errors in left-right(x),superior-inferior(y)and anteriorposterior(z)directions were obtained by the registration between the automatically reconstructed images and the planned CT image.Moreover,the margins of planning target areas were also calculated.Results Atotal of 3 128 CBCT scans were performed on all patients,including 1 679 scans in prone position and 1 449 scans in supine positions.In 981 scans(31.36%),the error of any axis(x,y,z)was less than 0.3 cm;and in 415 scans(13.27%),the deviation distance from the ioscenter was found to be less than 0.3 cm.When the error direction was considered,the setup errors in x,y and z directions were(0.109 5±0.380 7),(-0.035 1±0.569 2),(0.075 1±0.285 2)cm for prone position,and(0.001 1±0.303 4),(0.118 4±0.583 0),(0.033 2±0.248 0)cm for supine position.When the size of the setup error was considered,the setup errors in x,y and z directions were(0.300 8±0.257 7),(0.442 8±0.359 2),(0.227 1±0.188 2)cm for prone position,and(0.229 3±0.198 6),(0.470 2±0.364 4),(0.183 2±0.170 3)cm for supine position.The margins of planning target area in x,y,z directions were 0.540,0.486,0.387 cm for prone position and 0.215,0.704,0.257 cm for supine position.Conclusion The setup errors of the patients with uterine neoplasms who are in supine versus prone position have differences.The deviation distance from the ioscenter less than 0.3 cm should be used for the calibration of setup errors.The margins of target areas in x,y,z directions are 0.540,0.486,0.387 cm for prone position,and 0.215,0.704,0.257 cm for supine position.