title: Preliminary clinical evaluation of a 4D-CBCT estimation technique using prior information and limited-angle projections.
abstract: OBJECTIVE
  A technique has been previously reported to estimate high-quality 4D-CBCT using prior information and limited-angle projections. This study is to investigate its clinical feasibility through both phantom and patient studies.
  
  
  METHODS
  The new technique used to estimate 4D-CBCT is called MMFD-NCC. It is based on the previously reported motion modeling and free-form deformation (MMFD) method, with the introduction of normalized-cross-correlation (NCC) as a new similarity metric. The clinical feasibility of this technique was evaluated by assessing the accuracy of estimated anatomical structures in comparison to those in the 'ground-truth' reference 4D-CBCTs, using data obtained from a physical phantom and three lung cancer patients. Both volume percentage error (VPE) and center-of-mass error (COME) of the estimated tumor volume were used as the evaluation metrics.
  
  
  RESULTS
  The average VPE/COME of the tumor in the prior image was 257.1%/10.1 mm for the phantom study and 55.6%/3.8 mm for the patient study. Using only orthogonal-view 30° projections, the MMFD-NCC has reduced the corresponding values to 7.7%/1.2 mm and 9.6%/1.1 mm, respectively.
  
  
  CONCLUSIONS
  The MMFD-NCC technique is able to estimate 4D-CBCT images with geometrical accuracy of the tumor within 10% VPE and 2 mm COME, which can be used to improve the localization accuracy of radiotherapy.
authors.affiliation: Medical Physics Graduate Program, Duke University, Durham, USA. Electronic address: you.zhang@duke.edu.
authors.forename: You
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Medical Physics Graduate Program, Duke University, Durham, USA; Department of Radiation Oncology, Duke University Medical Center, Durham, USA.
authors.forename: Fang-Fang
authors.initials: FF
authors.lastname: Yin
authors.affiliation: Department of Imaging Physics, The University of Texas, MD Anderson Cancer Center, Houston, USA.
authors.forename: Tinsu
authors.initials: T
authors.lastname: Pan
authors.affiliation: Department of Radiation Oncology, Duke University Medical Center, Durham, USA.
authors.forename: Irina
authors.initials: I
authors.lastname: Vergalasova
authors.affiliation: Medical Physics Graduate Program, Duke University, Durham, USA; Department of Radiation Oncology, Duke University Medical Center, Durham, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Ren
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000295:instrumentation / Q000379:methods*; D056973:Four-Dimensional Computed Tomography / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D009038:Motion; D019047:Phantoms, Imaging
keywords: 4D-CBCT; Free-form deformation; Image estimation; Motion modeling
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