title: External validation of a prognostic model estimating the survival of patients with recurrent high-grade gliomas after reirradiation.
abstract: OBJECTIVE
  We aimed to validate a controversial prognostic model for the survival of relapsed malignant glioma patients after reirradiation with an independent, multicentric patient cohort.
  
  
  METHODS
  A total of 165 malignant glioma patients underwent reirradiation at 4 different institutions between 1994 and 2012. Twenty-two patients had a good (score 1), 44 had a moderate (score 2), and 99 had a poor prognosis (score 3 or 4). Four statistical methods were used to validate the prognostic model: First, we compared survival according to prognostic group in the construction and the validation cohort by visual comparison of the respective Kaplan-Meier plots. Second, discrimination was quantified by calculating hazard ratios for death for each prognostic group, with the worst prognostic group serving as the reference. Calibration was assessed by a calibration plot for the time point 12 months after reirradiation. Finally, we compared the predictive performance of the score and a hypothetical prognostic model ignoring all predictor variables over time by means of a prediction error curve.
  
  
  RESULTS
  On visual validation, the survival curves of the 3 patient groups with good, moderate, and poor prognoses nicely separated from each other. Median survival rates after reirradiation were 17.9, 9.0, and 7.7 months in the patient groups with good, moderate, and poor prognosis, respectively. Hazard ratios confirmed satisfactory discrimination. Calibration was satisfactory for all and most accurate for the worst prognostic group. The score improved the prognostic performance in comparison to the "zero-model."
  
  
  CONCLUSIONS
  We successfully validated a prognostic model for the survival of malignant glioma patients after reirradiation with a multicentric, independent dataset. Being reliable and easy to handle, the model can be useful in personalized patient counseling and clinical decision-making.
authors.affiliation: Department of Radiation Oncology, University of Leipzig Medical Center, Leipzig, Germany. Electronic address: Klaus.Mueller@medizin.uni-leipzig.de.
authors.forename: Klaus
authors.initials: K
authors.lastname: Müller
authors.affiliation: Department of Radiation Oncology, Cantonal Hospital St. Gallen, St. Gallen, Switzerland; Department of Radiooncology, University Hospital Tübingen, Tübingen, Germany.
authors.forename: Guido
authors.initials: G
authors.lastname: Henke
authors.affiliation: Department of Radiation Oncology (MAASTRO), GROW (School for Oncology & Developmental Biology), Maastricht University Medical Centre, Maastricht, The Netherlands.
authors.forename: Inge
authors.initials: I
authors.lastname: Compter
authors.affiliation: Department of Pediatrics and Adolescent Medicine, Division of Pediatric Hematology and Oncology, University Medical Center Goettingen, Goettingen, Germany.
authors.forename: André O
authors.initials: AO
authors.lastname: von Bueren
authors.affiliation: Division of Pediatric Oncology, Hematology and Hemostaseology, Department of Woman's and Children's Health, University Hospital Leipzig, Leipzig, Germany.
authors.forename: Carsten
authors.initials: C
authors.lastname: Friedrich
authors.affiliation: Department of Radiation Oncology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: Geert
authors.initials: G
authors.lastname: Janssens
authors.affiliation: Department of Pediatrics and Adolescent Medicine, Division of Pediatric Hematology and Oncology, University Medical Center Goettingen, Goettingen, Germany.
authors.forename: Christof M
authors.initials: CM
authors.lastname: Kramm
authors.affiliation: Departments of Neurology and Haematology/Oncology, Cantonal Hospital St. Gallen, St. Gallen, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hundsberger
authors.affiliation: Department of Radiooncology, University Hospital Tübingen, Tübingen, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Paulsen
authors.affiliation: Department of Radiation Oncology, University of Leipzig Medical Center, Leipzig, Germany.
authors.forename: Rolf-Dieter
authors.initials: RD
authors.lastname: Kortmann
authors.affiliation: Institute for Medical Biostatistics, Epidemiology and Informatics, University Medical Center Mainz, Mainz, Germany.
authors.forename: Isabella
authors.initials: I
authors.lastname: Zwiener
authors.affiliation: Department of Radiation Oncology (MAASTRO), GROW (School for Oncology & Developmental Biology), Maastricht University Medical Centre, Maastricht, The Netherlands; Department of Radiation Oncology, MediClin Robert Janker Clinic & University of Bonn Med Centre, Clinical Cooperation Unit Neurooncology, Bonn, Germany.
authors.forename: Brigitta G
authors.initials: BG
authors.lastname: Baumert
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000401:mortality* / Q000473:pathology / Q000532:radiotherapy*; D002138:Calibration; D002648:Child; D015331:Cohort Studies; D005910:Glioma / Q000401:mortality* / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D053208:Kaplan-Meier Estimate; D008875:Middle Aged; D008962:Models, Theoretical; D011379:Prognosis; D000069475:Re-Irradiation; D015996:Survival Rate; D055815:Young Adult