title: Absorbed dose and image quality of Varian TrueBeam CBCT compared with OBI CBCT.
abstract: OBJECTIVE
  Nowadays, patient positioning and target localization can be verified by using kilovolt cone beam computed tomography (kV-CBCT). There have been various studies on the absorbed doses and image qualities of different kV-CBCT systems. However, the Varian TrueBeam CBCT (TB CBCT) system has not been investigated so far. We assess the image quality and absorbed dose of TB CBCT through comparison with those of on-board imager (OBI) CBCT.
  
  
  METHODS
  The image quality was evaluated using two phantoms. A CATPHAN phantom measured the image quality parameters of the American Association of Physicists in Medicine Task Group 142 (AAPM TG-142) report. These factors are the pixel value stability and accuracy, noise, high-contrast resolution, low-contrast resolution, and image uniformity. A H2SO4phantom was used to evaluate the image uniformity over a larger region than the CATPHAN phantom. In evaluating the absorbed dose, the radial dose profile and the patient organ doses at the prostate and rectum levels were evaluated.
  
  
  RESULTS
  The image quality parameters of AAPM TG-142 using TB CBCT are equal to or greater than those of OBI CBCT. In particular, the contrast-to-noise ratio with TB CBCT is 2.5 times higher than that with OBI CBCT. For the test of a large field uniformity, the maximum difference in the Hounsfield unit (HU) values between the centre and peripheral regions is within 30 HU with TB CBCT and 283 HU with OBI CBCT. The maximum absorbed dose with TB CBCT is decreased by 60%.
  
  
  CONCLUSIONS
  We find that the image quality improved and the absorbed dose decreased with TB CBCT in comparison to those with OBI CBCT. Its image uniformity is also superior over a larger scanning range.
authors.affiliation: Section of Radiation Therapy, Department of Clinical Support, Hiroshima University Hospital, Japan; Course of Medical and Dental Sciences, Graduate School of Biomedical & Health Sciences, Hiroshima University, Japan. Electronic address: daika99@hiroshima-u.ac.jp.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kawahara
authors.affiliation: Department of Radiation Oncology, Institute of Biomedical & Health Sciences, Hiroshima University, Japan.
authors.forename: Shuichi
authors.initials: S
authors.lastname: Ozawa
authors.affiliation: Section of Radiation Therapy, Department of Clinical Support, Hiroshima University Hospital, Japan.
authors.forename: Takeo
authors.initials: T
authors.lastname: Nakashima
authors.affiliation: Department of Radiation Oncology, Institute of Biomedical & Health Sciences, Hiroshima University, Japan.
authors.forename: Tatsuhiko
authors.initials: T
authors.lastname: Suzuki
authors.affiliation: Course of Medical and Dental Sciences, Graduate School of Biomedical & Health Sciences, Hiroshima University, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Tsuneda
authors.affiliation: Department of Nuclear Engineering and Management, School of Engineering, University of Tokyo, Japan.
authors.forename: Sodai
authors.initials: S
authors.lastname: Tanaka
authors.affiliation: Section of Radiation Therapy, Department of Clinical Support, Hiroshima University Hospital, Japan.
authors.forename: Yoshimi
authors.initials: Y
authors.lastname: Ohno
authors.affiliation: Department of Radiation Oncology, Institute of Biomedical & Health Sciences, Hiroshima University, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Murakami
authors.affiliation: Department of Radiation Oncology, Institute of Biomedical & Health Sciences, Hiroshima University, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Nagata
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006801:Humans; D019047:Phantoms, Imaging; D011786:Quality Control; D011829:Radiation Dosage
keywords: Absorbed dose; Cone-beam computed tomography; Image quality