title: Kilovoltage beam model for flat panel imaging system with bow-tie filter for scatter prediction and correction.
abstract: OBJECTIVE
  Kilovoltage flat-panel imaging systems are used for cone-beam Computed Tomography (CBCT) and digital Tomosynthesis (DTS). Hereby, the presence of scatter and relatively large dose from imaging are challenging factors. In this study a phenomenological beam model was developed to characterize imager response to imaging beams with a bow-tie filter (Varian OBI system).
  
  
  METHODS
  The kilovoltage beam model was based on dose ratio formalism and thus was using standard concepts of megavoltage dose calculation such as scatter factors, tissue maximum ratio and off-axis ratio. Primary and scatter (head and phantom scatter) were modeled with three Gaussian kernels. Parameters were based on measured transmission images for slabs of solid water of different total thickness and various jaw settings.
  
  
  RESULTS
  The beam model was used to evaluate contributions from primary, secondary and tertiary contributions for different geometrical objects such as cylinders and step-like phantoms. Theoretical predictions of radiographs using the model for known objects are consistent with the measurements.
  
  
  CONCLUSIONS
  Secondary and tertiary contributions were interpreted as scatter and can be subtracted from CBCT projections based on the analytical model. Therefore our model can provide a basis for improvement of image quality (less artifacts due to scatter, better contrast and resolution) in CBCT reconstruction.
authors.affiliation: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Mannheim, Germany. Manuel.blessing@urz.uni-heidelberg.de
authors.forename: M
authors.initials: M
authors.lastname: Blessing
authors.forename: M S
authors.initials: MS
authors.lastname: Bhagwat
authors.forename: Y
authors.initials: Y
authors.lastname: Lyatskaya
authors.forename: J R
authors.initials: JR
authors.lastname: Bellon
authors.forename: J
authors.initials: J
authors.lastname: Hesser
authors.forename: P
authors.initials: P
authors.lastname: Zygmanski
mesh_terms: D000388:Air; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008962:Models, Theoretical; D011829:Radiation Dosage; D015203:Reproducibility of Results; D012542:Scattering, Radiation