title: Interobserver variability of radiation therapists aligning to fiducial markers for prostate radiation therapy.
abstract: BACKGROUND
  As the use of fiducial markers (FMs) for the localisation of the prostate during external beam radiation therapy (EBRT) has become part of routine practice, radiation therapists (RTs) have become increasingly responsible for online image interpretation. The aim of this investigation was to quantify the limits of agreement (LoA) between RTs when localising to FMs with orthogonal kilovoltage (kV) imaging.
  
  
  METHODS
  Six patients receiving prostate EBRT utilising FMs were included in this study. Treatment localisation was performed using kV imaging prior to each fraction. Online stereoscopic assessment of FMs, performed by the treating RTs, was compared with the offline assessment by three RTs. Observer agreement was determined by pairwise Bland-Altman analysis.
  
  
  RESULTS
  Stereoscopic analysis of 225 image pairs was performed online at the time of treatment, and offline by three RT observers. Eighteen pairwise Bland-Altman analyses were completed to assess the level of agreement between observers. Localisation by RTs was found to be within clinically acceptable 95% LoAs.
  
  
  CONCLUSIONS
  Small differences between RTs, in both the online and offline setting, were found to be within clinically acceptable limits. RTs were able to make consistent and reliable judgements when matching FMs on planar kV imaging.
authors.affiliation: Radiation Oncology Mater Centre, Princess Alexandra Hospital, South Brisbane. Timothy_Deegan@health.qld.gov.au
authors.forename: Timothy
authors.initials: T
authors.lastname: Deegan
authors.forename: Rebecca
authors.initials: R
authors.lastname: Owen
authors.forename: Tanya
authors.initials: T
authors.lastname: Holt
authors.forename: Lisa
authors.initials: L
authors.lastname: Roberts
authors.forename: Jennifer
authors.initials: J
authors.lastname: Biggs
authors.forename: Alicia
authors.initials: A
authors.lastname: McCarthy
authors.forename: Matthew
authors.initials: M
authors.lastname: Parfitt
authors.forename: Andrew
authors.initials: A
authors.lastname: Fielding
mesh_terms: D057918:Fiducial Markers; D006801:Humans; D008297:Male; D015588:Observer Variation; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D020266:Radiotherapy, Conformal / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: fiducial marker; observer variability; radiation therapy