title: Contouring variability of the penile bulb on CT images: quantitative assessment using a generalized concordance index.
abstract: OBJECTIVE
  Within a multicenter study (DUE-01) focused on the search of predictors of erectile dysfunction and urinary toxicity after radiotherapy for prostate cancer, a dummy run exercise on penile bulb (PB) contouring on computed tomography (CT) images was carried out. The aim of this study was to quantitatively assess interobserver contouring variability by the application of the generalized DICE index.
  
  
  METHODS
  Fifteen physicians from different Institutes drew the PB on CT images of 10 patients. The spread of DICE values was used to objectively select those observers who significantly disagreed with the others. The analyses were performed with a dedicated module in the VODCA software package.
  
  
  RESULTS
  DICE values were found to significantly change among observers and patients. The mean DICE value was 0.67, ranging between 0.43 and 0.80. The statistics of DICE coefficients identified 4 of 15 observers who systematically showed a value below the average (p value range, 0.013 - 0.059): Mean DICE values were 0.62 for the 4 "bad" observers compared to 0.69 of the 11 "good" observers. For all bad observers, the main cause of the disagreement was identified. Average DICE values were significantly worse from the average in 2 of 10 patients (0.60 vs. 0.70, p < 0.05) because of the limited visibility of the PB. Excluding the bad observers and the "bad" patients," the mean DICE value increased from 0.67 to 0.70; interobserver variability, expressed in terms of standard deviation of DICE spread, was also reduced.
  
  
  CONCLUSIONS
  The obtained values of DICE around 0.7 shows an acceptable agreement, considered the small dimension of the PB. Additional strategies to improve this agreement are under consideration and include an additional tutorial of the so-called bad observers with a recontouring procedure, or the recontouring by a single observer of the PB for all patients included in the DUE-01 study.
authors.affiliation: Department of Medical Physics, San Raffaele Scientific Institute, Milano, Italy.
authors.forename: Viviana
authors.initials: V
authors.lastname: Carillo
authors.forename: Cesare
authors.initials: C
authors.lastname: Cozzarini
authors.forename: Lucia
authors.initials: L
authors.lastname: Perna
authors.forename: Mauro
authors.initials: M
authors.lastname: Calandra
authors.forename: Stefano
authors.initials: S
authors.lastname: Gianolini
authors.forename: Tiziana
authors.initials: T
authors.lastname: Rancati
authors.forename: Antonello Enrico
authors.initials: AE
authors.lastname: Spinelli
authors.forename: Vittorio
authors.initials: V
authors.lastname: Vavassori
authors.forename: Sergio
authors.initials: S
authors.lastname: Villa
authors.forename: Riccardo
authors.initials: R
authors.lastname: Valdagni
authors.forename: Claudio
authors.initials: C
authors.lastname: Fiorino
mesh_terms: D006801:Humans; D008297:Male; D015588:Observer Variation; D010413:Penis / Q000000981:diagnostic imaging*; D019047:Phantoms, Imaging; D012984:Software; D014057:Tomography, X-Ray Computed / Q000379:methods*