title: Daily online bony correction is required for prostate patients without fiducial markers or soft-tissue imaging.
abstract: OBJECTIVE
  To compare online position verification strategies with offline correction protocols for patients undergoing definitive prostate radiotherapy.
  
  
  METHODS
  We analysed 50 patients with implanted fiducial markers undergoing curative prostate radiation treatment, all of whom underwent daily kilovoltage imaging using an on-board imager. For each treatment, patients were set-up initially with skin tattoos and in-room lasers. Orthogonal on-board imager images were acquired and the couch shift to match both bony anatomy and the fiducial markers recorded. The set-up error using skin tattoos and offline bone correction was compared with online bone correction. The fiducial markers were used as the reference.
  
  
  RESULTS
  Data from 1923 fractions were analysed. The systematic error was ≤1 mm for all protocols. The average random error was 2-3mm for online bony correction and 3-5mm for skin tattoos or offline-bone. Online-bone showed a significant improvement compared with offline-bone in the number of patients with >5mm set-up errors for >10% (P<0.001) and >20% (P<0.003) of their fractions.
  
  
  CONCLUSIONS
  Online correction to bony anatomy reduces both systematic and random set-up error in patients undergoing prostate radiotherapy, and is superior to offline correction methods for those patients not suitable for fiducial markers or daily soft-tissue imaging.
authors.affiliation: Northern Sydney Cancer Centre, Royal North Shore Hospital, Sydney, NSW, Australia.
authors.forename: M L
authors.initials: ML
authors.lastname: Johnston
authors.forename: P
authors.initials: P
authors.lastname: Vial
authors.forename: K L
authors.initials: KL
authors.lastname: Wiltshire
authors.forename: L J
authors.initials: LJ
authors.lastname: Bell
authors.forename: S
authors.initials: S
authors.lastname: Blome
authors.forename: Z
authors.initials: Z
authors.lastname: Kerestes
authors.forename: G W
authors.initials: GW
authors.lastname: Morgan
authors.forename: D
authors.initials: D
authors.lastname: O'Driscoll
authors.forename: T P
authors.initials: TP
authors.lastname: Shakespeare
authors.forename: T N
authors.initials: TN
authors.lastname: Eade
mesh_terms: D057918:Fiducial Markers; D006801:Humans; D008297:Male; D010384:Pelvic Bones / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D011881:Radiotherapy, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated; D012189:Retrospective Studies