title: Deformable planning CT to cone-beam CT image registration in head-and-neck cancer.
abstract: OBJECTIVE
  The purpose of this work was to implement and validate a deformable CT to cone-beam computed tomography (CBCT) image registration method in head-and-neck cancer to eventually facilitate automatic target delineation on CBCT.
  
  
  METHODS
  Twelve head-and-neck cancer patients underwent a planning CT and weekly CBCT during the 5-7 week treatment period. The 12 planning CT images (moving images) of these patients were registered to their weekly CBCT images (fixed images) via the symmetric force Demons algorithm and using a multiresolution scheme. Histogram matching was used to compensate for the intensity difference between the two types of images. Using nine known anatomic points as registration targets, the accuracy of the registration was evaluated using the target registration error (TRE). In addition, region-of-interest (ROI) contours drawn on the planning CT were morphed to the CBCT images and the volume overlap index (VOI) between registered contours and manually delineated contours was evaluated.
  
  
  RESULTS
  The mean TRE value of the nine target points was less than 3.0 mm, the slice thickness of the planning CT. Of the 369 target points evaluated for registration accuracy, the average TRE value was 2.6 +/- 0.6 mm. The mean TRE for bony tissue targets was 2.4 +/- 0.2 mm, while the mean TRE for soft tissue targets was 2.8 +/- 0.2 mm. The average VOI between the registered and manually delineated ROI contours was 76.2 +/- 4.6%, which is consistent with that reported in previous studies.
  
  
  CONCLUSIONS
  The authors have implemented and validated a deformable image registration method to register planning CT images to weekly CBCT images in head-and-neck cancer cases. The accuracy of the TRE values suggests that they can be used as a promising tool for automatic target delineation on CBCT.
authors.affiliation: Department of Radiation Oncology, University of Maryland School of Medicine, 22 South Greene Street, Baltimore, Maryland 21201, USA.
authors.forename: Jidong
authors.initials: J
authors.lastname: Hou
authors.forename: Mariana
authors.initials: M
authors.lastname: Guerrero
authors.forename: Wenjuan
authors.initials: W
authors.lastname: Chen
authors.forename: Warren D
authors.initials: WD
authors.lastname: D'Souza
mesh_terms: D000465:Algorithms; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D009038:Motion; D015203:Reproducibility of Results