title: Accuracy of UTE-MRI-based patient setup for brain cancer radiation therapy.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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™.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  UTE-MRI-based DRRs appear to be promising for daily patient setup of brain cancer radiotherapy with kV on-board imaging.
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California 90095.
authors.forename: Yingli
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California 90095.
authors.forename: Minsong
authors.initials: M
authors.lastname: Cao
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California 90095.
authors.forename: Tania
authors.initials: T
authors.lastname: Kaprealian
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California 90095.
authors.forename: Ke
authors.initials: K
authors.lastname: Sheng
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California 90095.
authors.forename: Yu
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Department of Radiological Sciences, University of California, Los Angeles, California 90095.
authors.forename: Fei
authors.initials: F
authors.lastname: Han
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California 90095.
authors.forename: Caitlin
authors.initials: C
authors.lastname: Gomez
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California 90095.
authors.forename: Anand
authors.initials: A
authors.lastname: Santhanam
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California 90095.
authors.forename: Stephen
authors.initials: S
authors.lastname: Tenn
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California 90095.
authors.forename: Nzhde
authors.initials: N
authors.lastname: Agazaryan
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California 90095.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Low
authors.affiliation: Department of Radiological Sciences, University of California, Los Angeles, California 90095.
authors.forename: Peng
authors.initials: P
authors.lastname: Hu
mesh_terms: D001932:Brain Neoplasms / Q000175:diagnosis / Q000532:radiotherapy*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D012680:Sensitivity and Specificity; D013997:Time Factors