title: Prostate cancer: prediction of biochemical failure after external-beam radiation therapy--Kattan nomogram and endorectal MR imaging estimation of tumor volume.
abstract: OBJECTIVE
  To determine whether magnetic resonance (MR) imaging and MR spectroscopic imaging findings can improve predictions made with the Kattan nomogram for radiation therapy.
  
  
  METHODS
  The institutional review board approved this retrospective HIPAA-compliant study. Ninety-nine men who underwent endorectal MR and MR spectroscopy before external-beam radiation therapy for prostate cancer (January 1998 to June 2007) were included. Linear predictors were calculated with input variables from the study sample and the Kattan original coefficients. The linear predictor is a single weighted value that combines information of all predictor variables in a model, where the weight of each value is its association with the outcome. Two radiologists independently reviewed all MR images to determine extent of disease; a third independent reader resolved discrepancies. Biochemical failure was defined as a serum prostate-specific antigen level of 2 ng/mL (2 μg/L) or more above nadir. Cox proportional hazard models were used to determine the probabilities of treatment failure (biochemical failure) in 5 years. One model included only the Kattan nomogram data; the other also incorporated imaging findings. The discrimination performance of all models was determined with receiver operating characteristics (ROC) curve analyses. These analyses were followed by an assessment of net risk reclassification.
  
  
  RESULTS
  The areas under the ROC curve for the Kattan nomogram and the model incorporating MR imaging findings were 61.1% (95% confidence interval: 58.1%, 64.0%) and 78.0% (95% confidence interval: 75.7%, 80.4%), respectively. Comparison of performance showed that the model with imaging findings performed significantly better than did the model with clinical variables alone (P < .001). Overall, the addition of imaging findings led to an improvement in risk classification of about 28%, ranging from approximately a minimum of 16% to a maximum of 39%, depending on the risk change considered important.
  
  
  CONCLUSIONS
  MR imaging data improve the prediction of biochemical failure with the Kattan nomogram after external-beam radiation therapy for prostate cancer. The number needed to image to improve the prediction of biochemical failure in one patient ranged from three to six.
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California San Francisco, 505 Parnassus Ave, Box 0628, Room M-372, San Francisco, CA 94143-0628, USA. antoniocarlos.westphalen@ucsf.edu
authors.forename: Antonio C
authors.initials: AC
authors.lastname: Westphalen
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Koff
authors.forename: Fergus V
authors.initials: FV
authors.lastname: Coakley
authors.forename: Valdair F
authors.initials: VF
authors.lastname: Muglia
authors.forename: John M
authors.initials: JM
authors.lastname: Neuhaus
authors.forename: Ralph T
authors.initials: RT
authors.lastname: Marcus
authors.forename: John
authors.initials: J
authors.lastname: Kurhanewicz
authors.forename: Rebecca
authors.initials: R
authors.lastname: Smith-Bindman
mesh_terms: D000368:Aged; D000465:Algorithms; D018450:Disease Progression; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D008875:Middle Aged; D049451:Nomograms; D011237:Predictive Value of Tests; D016016:Proportional Hazards Models; D017430:Prostate-Specific Antigen / Q000097:blood; D011471:Prostatic Neoplasms / Q000097:blood / Q000473:pathology / Q000532:radiotherapy*; D012372:ROC Curve; D012189:Retrospective Studies; D015996:Survival Rate; D047368:Tumor Burden
chemical_list: D017430:Prostate-Specific Antigen