title: Evaluating the image quality of cone beam CT acquired during rotational delivery.
abstract: OBJECTIVE
  The aim of this work was to evaluate the quality of kilovoltage (kV) cone beam CT (CBCT) images acquired during arc delivery.
  
  
  METHODS
  Arc plans were delivered on a Catphan(®) 600 phantom (The Phantom Laboratory Inc., Salem, NY), and kV CBCT images were acquired during the treatment. The megavoltage (MV) scatter effect on kV CBCT image quality was evaluated using parameters such as Hounsfield unit (HU) accuracy, spatial resolution, contrast-to-noise ratio (CNR) and spatial non-uniformity (SNU). These CBCT images were compared with reference scans acquired with the same acquisition parameters without MV "beam on". This evaluation was carried out for different photon beams (6 and 15 MV), arc types (half vs full arc), static field sizes (10 × 10 and 25 × 25 cm(2)) and source-to-imager distances (SID) (150 and 170 cm).
  
  
  CONCLUSIONS
  HU accuracy, CNR and SNU were considerably affected by MV scatter, and this effect was increased with increasing field size and decreasing photon energy, whereas the spatial resolution was almost unchanged. The MV scatter effect was observed to be more for full-rotation arc delivery than for half-arc delivery. In addition, increasing the SID resulted in decreased MV scatter effect and improved the image quality.
  
  
  CONCLUSIONS
  Nowadays, volumetric modulated arc therapy (VMAT) is increasingly used in clinics, and this arc therapy enables us to acquire CBCT imaging simultaneously. But, the main issue of concurrent imaging is the "MV scatter" effect on CBCT imaging. This study aims to experimentally quantify the effect of MV scatter on CBCT image quality.
authors.affiliation: 1 Department of Radiotherapy, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India.
authors.forename: S A
authors.initials: SA
authors.lastname: Yoganathan
authors.affiliation: 1 Department of Radiotherapy, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India.
authors.forename: K J
authors.initials: KJ
authors.lastname: Maria Das
authors.affiliation: 2 Department of Medical Physics, Anna University, Chennai, Tamil Nadu, India.
authors.forename: K
authors.initials: K
authors.lastname: Maria Midunvaleja
authors.affiliation: 1 Department of Radiotherapy, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India.
authors.forename: D
authors.initials: D
authors.lastname: Gowtham Raj
authors.affiliation: 1 Department of Radiotherapy, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India.
authors.forename: Arpita
authors.initials: A
authors.lastname: Agarwal
authors.affiliation: 2 Department of Medical Physics, Anna University, Chennai, Tamil Nadu, India.
authors.forename: J
authors.initials: J
authors.lastname: Velmurugan
authors.affiliation: 1 Department of Radiotherapy, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India.
authors.forename: Shaleen
authors.initials: S
authors.lastname: Kumar
mesh_terms: D000465:Algorithms; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006801:Humans; D019047:Phantoms, Imaging; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*