title: The effect of delineation method and observer variability on bladder dose-volume histograms for prostate intensity modulated radiotherapy.
abstract: OBJECTIVE
  To quantify the effect of delineation method on bladder DVH, observer variability (OV) and contouring time for prostate IMRT plans.
  
  
  METHODS
  Planning CT scans and IMRT plans of 30 prostate cancer patients were anonymized. For 20 patients, 1 observer delineated the bladder using 9 methods. The effect of delineation method on the DVH curve, discrete dose levels and delineation time was quantified. For the 10 remaining CTs, 6 observers delineated bladder wall using 4 methods. Observer-based volume variation and intraclass correlation coefficient (ICC) were used to describe the dosimetric effects of OV.
  
  
  RESULTS
  Manual delineation of the bladder wall (BW_m) was significantly slower than any other method (mean: 20 min vs. ≤ 13 min) and the dosimetric effect of OV was significantly larger (V70 Gy ICC: 0.78 vs. 0.98). Only volumes created using a 2.5mm contraction from the outer surface, and a method providing a consistent wall volume, showed no notable dosimetric differences from BW_m in both absolute and relative volume.
  
  
  CONCLUSIONS
  Automatic contractions from the outer surface provide quicker, more reproducible and reasonably accurate substitutes for BW_m. The widespread use of automatic contractions to create a bladder wall volume would assist in the consistent application of IMRT dose constraints and the interpretation of reported dose.
authors.affiliation: Princess Margaret Hospital and Department of Radiation Oncology, University of Toronto, Canada. Tara.Rosewall@rmp.uhn.on.ca
authors.forename: Tara
authors.initials: T
authors.lastname: Rosewall
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Bayley
authors.forename: Peter
authors.initials: P
authors.lastname: Chung
authors.forename: Lisa W
authors.initials: LW
authors.lastname: Le
authors.forename: Jason
authors.initials: J
authors.lastname: Xie
authors.forename: Siddhartha
authors.initials: S
authors.lastname: Baxi
authors.forename: Charles N
authors.initials: CN
authors.lastname: Catton
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Currie
authors.forename: Janelle
authors.initials: J
authors.lastname: Wheat
authors.forename: Michael
authors.initials: M
authors.lastname: Milosevic
mesh_terms: D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated; D012189:Retrospective Studies; D001743:Urinary Bladder / Q000528:radiation effects*