title: Automatic registration of portal images and volumetric CT for patient positioning in radiation therapy.
abstract: The efficacy of radiation therapy treatment depends on the patient setup accuracy at each daily fraction. A significant problem is reproducing the patient position during treatment planning for every fraction of the treatment process. We propose and evaluate an intensity based automatic registration method using multiple portal images and the pre-treatment CT volume. We perform both geometric and radiometric calibrations to generate high quality digitally reconstructed radiographs (DRRs) that can be compared against portal images acquired right before treatment dose delivery. We use a graphics processing unit (GPU) to generate the DRRs in order to gain computational efficiency. We also perform a comparative study on various similarity measures and optimization procedures. Simple similarity measure such as local normalized correlation (LNC) performs best as long as the radiometric calibration is carefully done. Using the proposed method, we achieved better than 1mm average error in repositioning accuracy for a series of phantom studies using two open field (i.e., 41 cm2) portal images with 90 degrees vergence angle.
authors.affiliation: Imaging and Visualization Department, Siemens Corporate Research, Inc., 755 College Road East, Princeton, NJ 08540, USA. akhamene@scr.siemens.com
authors.forename: Ali
authors.initials: A
authors.lastname: Khamene
authors.forename: Peter
authors.initials: P
authors.lastname: Bloch
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wein
authors.forename: Michelle
authors.initials: M
authors.lastname: Svatos
authors.forename: Frank
authors.initials: F
authors.lastname: Sauer
mesh_terms: D000465:Algorithms; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D019047:Phantoms, Imaging; D011187:Posture; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D013223:Statistics as Topic; D014057:Tomography, X-Ray Computed