title: Comparison of localization performance with implanted fiducial markers and cone-beam computed tomography for on-line image-guided radiotherapy of the prostate.
abstract: OBJECTIVE
  The aim of this work was to assess the accuracy of kilovoltage (kV) cone-beam computed tomography (CBCT)-based setup corrections as compared with orthogonal megavoltage (MV) portal image-based corrections for patients undergoing external-beam radiotherapy of the prostate.
  
  
  METHODS
  Daily cone-beam CT volumetric images were acquired after setup for patients with three intraprostatic fiducial markers. The estimated couch shifts were compared retrospectively to patient adjustments based on two orthogonal MV portal images (the current clinical standard of care in our institution). The CBCT soft-tissue based shifts were also estimated by digitally removing the gold markers in each projection to suppress the artifacts in the reconstructed volumes. A total of 256 volumetric images for 15 patients were analyzed.
  
  
  RESULTS
  The Pearson coefficient of correlation for the patient position shifts using fiducial markers in MV vs. kV was (R2 = 0.95, 0.84, 0.81) in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions, respectively. The correlation using soft-tissue matching was as follows: R2 = 0.90, 0.49, 0.51 in the LR, AP and SI directions. A Bland-Altman analysis showed no significant trends in the data. The percentage of shifts within a +/-3-mm tolerance (the clinical action level) was 99.7%, 95.5%, 91.3% for fiducial marker matching and 99.5%, 70.3%, 78.4% for soft-tissue matching.
  
  
  CONCLUSIONS
  Cone-beam CT is an accurate and precise tool for image guidance. It provides an equivalent means of patient setup correction for prostate patients with implanted gold fiducial markers. Use of the additional information provided by the visualization of soft-tissue structures is an active area of research.
authors.affiliation: Radiation Medicine Program, Princess Margaret Hospital, Toronto, ON, Canada. douglas.moseley@rmp.uhn.on.ca
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Moseley
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: White
authors.forename: Kirsty L
authors.initials: KL
authors.lastname: Wiltshire
authors.forename: Tara
authors.initials: T
authors.lastname: Rosewall
authors.forename: Michael B
authors.initials: MB
authors.lastname: Sharpe
authors.forename: Jeffrey H
authors.initials: JH
authors.lastname: Siewerdsen
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Bissonnette
authors.forename: Mary
authors.initials: M
authors.lastname: Gospodarowicz
authors.forename: Padraig
authors.initials: P
authors.lastname: Warde
authors.forename: Charles N
authors.initials: CN
authors.lastname: Catton
authors.forename: David A
authors.initials: DA
authors.lastname: Jaffray
mesh_terms: D016477:Artifacts; D005240:Feasibility Studies; D006046:Gold; D006801:Humans; D008297:Male; D015588:Observer Variation; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D019736:Prostheses and Implants; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D006046:Gold