title: A gradient feature weighted Minimax algorithm for registration of multiple portal images to 3DCT volumes in prostate radiotherapy.
abstract: OBJECTIVE
  To develop an accurate, fast, and robust algorithm for registering portal and computed tomographic (CT) images for radiotherapy using a combination of sparse and dense field data that complement each other.
  
  
  METHODS
  Gradient Feature Weighted Minimax (GFW Minimax) method was developed to register multiple portal images to three-dimensional CT images. Its performance was compared with that of three others: Minimax, Mutual Information, and Gilhuijs' method. Phantom and prostate cancer patient images were used. Effects of registration errors on tumor control probability (TCP) and normal tissue complication probability (NTCP) were investigated as a relative measure.
  
  
  RESULTS
  Registration of four portals to CTs resulted in 30% lower error when compared with registration with two portals. Computation time increased by nearly 50%. GFW Minimax performed the best, followed by Gilhuijs' method, the Minimax method, and Mutual Information.
  
  
  CONCLUSIONS
  Using four portals instead of two lowered the registration error. Reduced fields of view images with full feature sets gave similar results in shorter times as full fields of view images. In clinical situations where soft tissue targets are of importance, GFW Minimax algorithm was significantly more accurate and robust. With registration errors lower than 1 mm, margins may be scaled down to 4 mm without adversely affecting TCP and NTCP.
authors.affiliation: Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, CT.
authors.forename: Sudhakar
authors.initials: S
authors.lastname: Chelikani
authors.forename: Kailasnath
authors.initials: K
authors.lastname: Purushothaman
authors.forename: Jonathan
authors.initials: J
authors.lastname: Knisely
authors.forename: Zhe
authors.initials: Z
authors.lastname: Chen
authors.forename: Ravinder
authors.initials: R
authors.lastname: Nath
authors.forename: Ravi
authors.initials: R
authors.lastname: Bansal
authors.forename: James
authors.initials: J
authors.lastname: Duncan
mesh_terms: D000465:Algorithms; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D019047:Phantoms, Imaging; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D011859:Radiography