title: Three-dimensional anatomy setup verification by correlation of orthogonal portal images and digitally reconstructed radiographs.
abstract: A method for three-dimensional verification of anatomy setup that uses the correlation of portal images and reference megavoltage digitally reconstructed radiographs (MDRRs) is presented. Prior to a treatment, an orthogonal pair of portal images is acquired from which subimages containing anatomical features are selected. These subimages are consequently matched to MDRRs that represent different rotations of the anatomy around axes going through the treatment isocenter. The Pearson correlation coefficient is employed for the matching since it is invariant with respect to global scaling and shifting of the image intensities. Furthermore, it does not require feature extraction or point-pair identification. The greatest value of the correlation coefficient corresponds to the proper rotational alignment of the anatomy and the location of the correlation maximum in each view indicates the translational shifts of the anatomy. The mean accuracy of translation and rotation registrations tests were a fraction of a millimeter and a fraction of a degree, respectively, for MDRR-to-MDRR matching. For portal-to-MDRR matching, the mean translation registration error is on the order of 1 mm and the mean error in radial displacement is of the order of 2.7 mm.
authors.affiliation: Medical Physics Unit, McGill University, Montreal General Hospital, Quebec, Canada.
authors.forename: L M
authors.initials: LM
authors.lastname: Sirois
authors.forename: D H
authors.initials: DH
authors.lastname: Hristov
authors.forename: B G
authors.initials: BG
authors.lastname: Fallone
mesh_terms: D000465:Algorithms; D016208:Databases, Factual; D005240:Feasibility Studies; D005583:Fourier Analysis; D006801:Humans; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D011187:Posture; D011856:Radiographic Image Enhancement / Q000379:methods*; D011882:Radiotherapy, High-Energy / Q000379:methods*; D014057:Tomography, X-Ray Computed