title: Prediction of gastrointestinal toxicity after external beam radiotherapy for localized prostate cancer.
abstract: BACKGROUND
  Gastrointestinal (GI) toxicity is a common effect following radiation therapy (RT) for prostate cancer. Purpose of the present work is to compare two Normal Tissue Complication Probability (NTCP) modelling approaches for prediction of late radio-induced GI toxicity after prostate external beam radiotherapy.
  
  
  METHODS
  The study includes 84 prostate cancer patients evaluated for late rectal toxicity after 3D conformal radiotherapy. Median age was 72 years (range 53-85). All patients received a total dose of 76 Gy to the prostate gland with daily fractions of 2 Gy. The acute and late radio-induced GI complications were classified according to the RTOG/EORTC scoring system. Rectum dose-volume histograms were extracted for Lyman-Kutcher-Burman (LKB) NTCP model fitting using Maximum Likelihood Estimation. The bootstrap method was employed to test the fit robustness. The area under the receiver operating characteristic curve (AUC) was used to evaluate the predictive power of the LKB and to compare it with a multivariate logistic NTCP model previously determined.
  
  
  RESULTS
  At a median follow-up of 36 months, 42% (35/84) of patients experienced grade 1-2 (G1-2) acute GI events while 25% (21/84) of patients developed G1-2 late GI events. The best-estimate of fitting parameters for LKB NTCP model for mild\moderate GI toxicity resulted to be: D 50  = 87.3 Gy, m = 0.37 and n = 0.10. Bootstrap result showed that the parameter fit was robust. The AUC values for the LKB and for the multivariate logistic models were 0.60 and 0.75, respectively.
  
  
  CONCLUSIONS
  We derived the parameters of the LKB model for mild\moderate GI toxicity prediction and we compared its performance with that of a data-driven multivariate model. Compared to LKB, the multivariate model confirmed a higher predictive power as showed by the AUC values.
authors.affiliation: Institute of Biostructure and Bioimaging, National Council of Research (CNR), Naples, Italy. vittoria.davino@ibb.cnr.it.
authors.forename: Vittoria
authors.initials: V
authors.lastname: D'Avino
authors.affiliation: Institute of Biostructure and Bioimaging, National Council of Research (CNR), Naples, Italy. giuseppe.palma@ibb.cnr.it.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Palma
authors.affiliation: Institute of Biostructure and Bioimaging, National Council of Research (CNR), Naples, Italy. raffaele.liuzzi@cnr.it.
authors.forename: Raffaele
authors.initials: R
authors.lastname: Liuzzi
authors.affiliation: Department of Advanced Biomedical Sciences, Federico II University School of Medicine, Naples, Italy. m.conson@gmail.com.
authors.forename: Manuel
authors.initials: M
authors.lastname: Conson
authors.affiliation: Department of Advanced Biomedical Sciences, Federico II University School of Medicine, Naples, Italy. Francydoria@libero.it.
authors.forename: Francesca
authors.initials: F
authors.lastname: Doria
authors.affiliation: Department of Advanced Biomedical Sciences, Federico II University School of Medicine, Naples, Italy. marsalva@unina.it.
authors.forename: Marco
authors.initials: M
authors.lastname: Salvatore
authors.affiliation: Department of Advanced Biomedical Sciences, Federico II University School of Medicine, Naples, Italy. roberto.pacelli@unina.it.
authors.forename: Roberto
authors.initials: R
authors.lastname: Pacelli
authors.affiliation: Institute of Biostructure and Bioimaging, National Council of Research (CNR), Naples, Italy. laura.cella@cnr.it.
authors.forename: Laura
authors.initials: L
authors.lastname: Cella
mesh_terms: D000368:Aged; D005767:Gastrointestinal Diseases / Q000175:diagnosis* / Q000209:etiology; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D012372:ROC Curve; D011832:Radiation Injuries / Q000175:diagnosis* / Q000209:etiology; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects*