title: Effect of dose reduction on image registration and image quality for cone-beam CT in radiotherapy.
abstract: BACKGROUND
  The additional radiation exposure applied to patients undergoing cone-beam computed tomography (CBCT) for image registration in radiation therapy is of great concern. Since a decrease in CBCT dose is linked to a degradation of image quality, the consequences of dose reduction on the registration process have to be investigated.
  
  
  METHODS
  This paper examines image quality and registration of low-contrast structures on an Elekta XVI for the two treatment areas prostate and chest while gradually decreasing the mAs per frame and the number of projections per CBCT to achieve dose reduction.
  
  
  RESULTS
  Ideal results for image quality were obtained for 1.6 mAs/frame and 377 projections in prostate scans and 0.63 mAs/frame and 440 projections in chest images. Lower as well as higher total mAs lead to a decrease in image quality. In spite of poor image quality, registration can be successfully performed even for lowest possible settings.
  
  
  CONCLUSIONS
  The results for registration allow an extensive dose reduction in both treatment areas. Very low mAs, however, do not qualify for clinical use because subjective judgment of the registration process is impossible. Compared to default presets the use of settings for acceptable image quality already permit a decrease in exposure of about 40 % (29.0 to 16.7 mGy) in prostate scans and 60 % (18.3 to 7.7 mGy) in chest scans.
authors.affiliation: Klinik für Strahlentherapie und Onkologie, Universitätsklinikum Frankfurt, Theodor-Stern-Kai 7, 60590, Frankfurt am Main, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Loutfi-Krauss
authors.forename: J
authors.initials: J
authors.lastname: Köhn
authors.forename: N
authors.initials: N
authors.lastname: Blümer
authors.forename: K
authors.initials: K
authors.lastname: Freundl
authors.forename: T
authors.initials: T
authors.lastname: Koch
authors.forename: E
authors.initials: E
authors.lastname: Kara
authors.forename: C
authors.initials: C
authors.lastname: Scherf
authors.forename: C
authors.initials: C
authors.lastname: Rödel
authors.forename: U
authors.initials: U
authors.lastname: Ramm
authors.forename: J
authors.initials: J
authors.lastname: Licher
mesh_terms: D000465:Algorithms; D054893:Cone-Beam Computed Tomography / Q000379:methods* / Q000592:standards; D005240:Feasibility Studies; D006801:Humans; D007089:Image Enhancement; D008297:Male; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011829:Radiation Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods* / Q000592:standards; D013899:Thoracic Neoplasms / Q000473:pathology / Q000532:radiotherapy*