title: Investigation of bladder dose and volume factors influencing late urinary toxicity after external beam radiotherapy for prostate cancer.
abstract: BACKGROUND
  We sought to identify the bladder dose-volume factors associated with an increased risk of late urinary toxicity among prostate cancer patients treated with radiotherapy.
  
  
  METHODS
  This retrospective analysis included data from 128 prostate cancer patients treated on protocol with 2 Gy/fraction to 46 Gy followed by a boost to 78 Gy. The endpoint for this analysis was Grade 1 or greater late genitourinary (GU) toxicity occurring within two years of treatment. The Lyman-Kutcher-Burman, mean dose, threshold dose, and hottest volume models were fitted to the toxicity data using the maximum likelihood method.
  
  
  RESULTS
  Model fits based on dose-volume histograms tended to fit the toxicity data better than models based on dose-wall histograms. The hottest volume (hotspot) model was found to be the best-fitting model investigated. The best fit was for the hottest 2.9% of bladder (95% CI, 1.1-6.8%). This model has an area under the receiver operating characteristic curve of 0.74. The hotspot model separated the patients into clinically meaningful subgroups with approximately 25% of the patients who received <78 Gy to the hottest 2.9% of bladder had GU toxicity at eight years compared with approximately 50% when the dose was > or =78 Gy (p = 0.002).
  
  
  CONCLUSIONS
  This provides the first evidence supporting that bladder "hotspots" are related to GU toxicity within two years after external beam radiotherapy for prostate cancer. Confirming data are needed from other investigators. Particular attention should be given to hotspots higher than 78 Gy in bladder in radiation treatment planning.
authors.affiliation: Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA. mrcheung@mdanderson.org
authors.forename: M Rex
authors.initials: MR
authors.lastname: Cheung
authors.forename: Susan L
authors.initials: SL
authors.lastname: Tucker
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
authors.forename: Renaud
authors.initials: R
authors.lastname: de Crevoisier
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Lee
authors.forename: Steven
authors.initials: S
authors.lastname: Frank
authors.forename: Rajat J
authors.initials: RJ
authors.lastname: Kudchadker
authors.forename: Howard
authors.initials: H
authors.lastname: Thames
authors.forename: Radhe
authors.initials: R
authors.lastname: Mohan
authors.forename: Deborah
authors.initials: D
authors.lastname: Kuban
mesh_terms: D000465:Algorithms; D006801:Humans; D016013:Likelihood Functions; D008297:Male; D015233:Models, Statistical; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000209:etiology; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000009:adverse effects; D012189:Retrospective Studies; D001743:Urinary Bladder / Q000033:anatomy & histology / Q000528:radiation effects*; D014555:Urination Disorders / Q000209:etiology*