Yang Yingli, Cao Minsong, Kaprealian Tania, Sheng Ke, Gao Yu, Han Fei, Gomez Caitlin, Santhanam Anand, Tenn Stephen, Agazaryan Nzhde, Low Daniel A, Hu Peng
Department of Radiation Oncology, University of California, Los Angeles, California 90095.
Department of Radiological Sciences, University of California, Los Angeles, California 90095.
Med Phys. 2016 Jan;43(1):262. doi: 10.1118/1.4938266.
Radiation therapy simulations solely based on MRI have advantages compared to CT-based approaches. One feature readily available from computed tomography (CT) that would need to be reproduced with MR is the ability to compute digitally reconstructed radiographs (DRRs) for comparison against on-board radiographs commonly used for patient positioning. In this study, the authors generate MR-based bone images using a single ultrashort echo time (UTE) pulse sequence and quantify their 3D and 2D image registration accuracy to CT and radiographic images for treatments in the cranium.
Seven brain cancer patients were scanned at 1.5 T using a radial UTE sequence. The sequence acquired two images at two different echo times. The two images were processed using an in-house software to generate the UTE bone images. The resultant bone images were rigidly registered to simulation CT data and the registration error was determined using manually annotated landmarks as references. DRRs were created based on UTE-MRI and registered to simulated on-board images (OBIs) and actual clinical 2D oblique images from ExacTrac™.
UTE-MRI resulted in well visualized cranial, facial, and vertebral bones that quantitatively matched the bones in the CT images with geometric measurement errors of less than 1 mm. The registration error between DRRs generated from 3D UTE-MRI and the simulated 2D OBIs or the clinical oblique x-ray images was also less than 1 mm for all patients.
UTE-MRI-based DRRs appear to be promising for daily patient setup of brain cancer radiotherapy with kV on-board imaging.
与基于CT的方法相比，仅基于MRI的放射治疗模拟具有优势。计算机断层扫描（CT）能够计算数字重建射线照相（DRR）以与常用于患者定位的机载射线照相进行比较，而这一功能需要通过MR来重现。在本研究中，作者使用单个超短回波时间（UTE）脉冲序列生成基于MR的骨骼图像，并量化其与CT及头颅治疗的射线图像的三维和二维图像配准精度。
对7例脑癌患者使用径向UTE序列在1.5T下进行扫描。该序列在两个不同回波时间采集两幅图像。使用内部软件对这两幅图像进行处理以生成UTE骨骼图像。将所得骨骼图像与模拟CT数据进行刚性配准，并以手动标注的地标为参考确定配准误差。基于UTE-MRI创建DRR，并将其与模拟的机载图像（OBI）以及来自ExacTrac™的实际临床二维斜位图像进行配准。
UTE-MRI生成的颅骨、面部和椎骨图像清晰可见，在几何测量误差小于1mm的情况下，其在数量上与CT图像中的骨骼相匹配。对于所有患者，由三维UTE-MRI生成的DRR与模拟的二维OBI或临床斜位X线图像之间的配准误差也小于1mm。
基于UTE-MRI的DRR在采用千伏级机载成像进行脑癌放射治疗的日常患者摆位方面似乎很有前景。
