title: 4D-CBCT reconstruction using MV portal imaging during volumetric modulated arc therapy.
abstract: BACKGROUND
  Recording target motion during treatment is important for verifying the irradiated region. Recently, cone-beam computed tomography (CBCT) reconstruction from portal images acquired during volumetric modulated arc therapy (VMAT), known as VMAT-CBCT, has been investigated. In this study, we developed a four-dimensional (4D) version of the VMAT-CBCT.
  
  
  METHODS
  The MV portal images were sequentially acquired from an electronic portal imaging device. The flex, background, monitor unit, field size, and multi-leaf collimator masking corrections were considered during image reconstruction. A 4D VMAT-CBCT requires a respiratory signal during image acquisition. An image-based phase recognition (IBPR) method was performed using normalised cross correlation to extract a respiratory signal from the series of portal images.
  
  
  RESULTS
  Our original IBPR method enabled us to reconstruct 4D VMAT-CBCT with no external devices. We confirmed that 4D VMAT-CBCT was feasible for two patients and in good agreement with in-treatment 4D kV-CBCT.
  
  
  CONCLUSIONS
  The visibility of the anatomy in 4D VMAT-CBCT reconstruction for lung cancer patients has the potential of using 4D VMAT-CBCT as a tool for verifying relative positions of tumour for each respiratory phase.
authors.affiliation: Department of Radiology, University of Tokyo Hospital, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kida
authors.forename: Naoya
authors.initials: N
authors.lastname: Saotome
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Masutani
authors.forename: Hideomi
authors.initials: H
authors.lastname: Yamashita
authors.forename: Kuni
authors.initials: K
authors.lastname: Ohtomo
authors.forename: Keiichi
authors.initials: K
authors.lastname: Nakagawa
authors.forename: Akira
authors.initials: A
authors.lastname: Sakumi
authors.forename: Akihiro
authors.initials: A
authors.lastname: Haga
mesh_terms: D000465:Algorithms; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D019583:Dose Fractionation, Radiation; D005240:Feasibility Studies; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D019047:Phantoms, Imaging; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration