Owen Rebecca, Kron Tomas, Foroudi Farshad, Milner Alvin, Cox Jennifer, Duchesne Gillian, Cleeve Laurence, Zhu Li, Cramb Jim, Sparks Laura, Laferlita Marcus
Radiation Therapy Services, Peter MacCallum Cancer Centre, Victoria, Australia.
Int J Radiat Oncol Biol Phys. 2009 Jul 1;74(3):906-12. doi: 10.1016/j.ijrobp.2009.01.054.
The objective of this investigation was to measure the agreement between in-room computed tomography (CT) on rails and electronic portal image (EPI) radiography.
Agreement between the location of the center of gravity (COG) of fiducial markers (FMs) on CT and EPI images was determined in phantom studies and a patient cohort. A secondary analysis between the center of volume (COV) of the prostate on CT and the COG of FMs on CT and EPI was performed. Agreement was defined as the 95% probability of a difference of <or=3.0 mm between images. Systematic and random errors from CT and EPI are reported.
From 8 patients, 254 CT and EPI pairs were analyzed. FMs were localized to within 3 mm on CT and EPI images 96.9% of the time in the left-right (LR) plane, 85.8% superior-inferior (SI), and 89% anterior-posterior (AP). The differences between the COV on CT and the COG on EPI were not within 3 mm in any plane: 87.8% (LR), 64.2% (SI), and 70.9% (AP). The systematic error varied from 1.2 to 2.9 mm (SI) and 1.8-2.9 mm (AP) between the COG on EPI and COV on CT.
Considerable differences between in-room CT and EPI exist. The phantom measurements showed slice thickness affected the accuracy of localization in the SI plane, and couch sag that occurs at the CT on rails gantry could not be totally corrected for in the AP plane. Other confounding factors are the action of rotating the couch and associated time lag between image acquisitions (prostate motion), EPI image quality, and outlining uncertainties.
本研究的目的是测量轨道式室内计算机断层扫描（CT）与电子射野影像（EPI）射线照相之间的一致性。
在体模研究和患者队列中确定CT和EPI图像上基准标记（FM）重心（COG）位置之间的一致性。对CT上前列腺的体积中心（COV）与CT和EPI上FM的COG进行了二次分析。一致性定义为图像之间差异≤3.0 mm的概率为95%。报告了CT和EPI的系统误差和随机误差。
对8例患者的254对CT和EPI图像进行了分析。在左右（LR）平面上，96.9%的时间内FM在CT和EPI图像上的定位误差在3 mm以内，在上下（SI）平面为85.8%，在前后（AP）平面为89%。CT上的COV与EPI上的COG在任何平面上的差异均不在3 mm以内：LR平面为87.8%，SI平面为64.2%，AP平面为70.9%。EPI上的COG与CT上的COV之间的系统误差在SI平面上为1.2至2.9 mm，在AP平面上为1.8至2.9 mm。
室内CT和EPI之间存在显著差异。体模测量显示，切片厚度影响了SI平面上的定位准确性，轨道式CT机架处发生的床身下垂在AP平面上无法完全校正。其他混杂因素包括床身旋转的影响以及图像采集之间的相关时间延迟（前列腺运动）、EPI图像质量和轮廓不确定性。
