磁共振引导放疗成像几何精度测试

Test for geometric accuracy of imaging for magnetic resonance-guided radiotherapy

目的:评估成像系统多因素尤其是图像几何精度对靶区和危及器官勾画的影响。方法:使用模体测试1.5T磁共振直线加速器系统的成像性能,包括磁共振图像几何失真评估以及由图像几何失真等因素引起的勾画偏差评估。使用Model 604-GS大场磁共振图像失真模体对磁共振引导放疗流程的磁共振图像进行几何失真度测试;同时使用CIRS Model008z上腹部模体进行相关靶区及OAR的勾画差异分析。结果:几何失真度结果显示,3DT1WI-FFE图像平均几何失真度0.54 mm,最大失真度1.96 mm;3DT2WI-TSE图像平均几何失真度0.53 mm,最大失真度1.68 mm,其中较大失真度的控制点分布于模体边缘,符合既往报道的磁共振图像特性。基于CT的勾画与基于3DT1WI-FFE和3DT2WI-TSE图像的勾画平均结果分别为MDA=1.17 mm,DSC=0.91;MDA=0.86 mm,DSC=0.94。结论:本研究定量评估了磁共振引导放疗成像系统的几何精度。基于仿真模拟人的勾画分析表明相对于CT图像,基于磁共振图像的勾画差异符合临床要求,同时3DT2WI-TSE图像在勾画精度相比于3DT1WI-FFE图像更有优势。

Objective To evaluate the effects of the multiple factors especially image geometric accuracy of the imaging system on the segmentations of target areas and organs-at-risk.Methods The study used phantoms to test the imaging performance of the 1.5T magnetic resonance(MR)linear accelerator system,including the assessments of MR image geometric distortion and the segmentation errors caused by factors such as image geometric distortion.Model 604-GS large field MR image distortion phantom was used to explore the geometric distortion of the MR images for MR-guided radiotherapy;and CIRS Model 008z upper abdominal phantom was used to analyze the segmentation errors of target areas and organs-at-risk.Results The average geometric distortion and maximum distortion of 3D T1WI-FFE images vs 3D T2WI-TSE images were 0.54 mm vs 0.53 mm and 1.96 mm vs 1.68 mm,respectively;and the control points of the large distortions were distributed at the edges of the phantom,which was consistent with the MR imaging characteristics previously reported.Compared with CT-based segmentation contour,the MDA was 1.17 mm and DSC was 0.91 for 3D T1WI-FFE,while MDA was 0.86 mm and DSC was 0.94 for 3D T2WI-TSE.Conclusion The study quantitatively assesses the geometric accuracy of the imaging system for MR-guided radiotherapy.The phantom-based contour analysis reveals that with CT image as gold standard,the segmentation error in MRI images meets the clinical requirements,and that 3D T2WI-TSE image is advantageous over 3D T1WI-FFE image in segmentation accuracy.