ESTRO 36 Abstract Book

S226 ESTRO 36 _______________________________________________________________________________________________

covariates and nomograms developed as a visual representation. The nomogram shows only significative covariates (p<=0.01). According to the TRIPOD [2], all Pms were validated using external validation of type 2b. The models performance was evaluated using the Area under the Receiver Operating Curve (AUC) and the brier score. Results Three thousand seven hundred seventy patients out of 7612 patients in this pooled dataset satisfied the inclusion criteria and were analyzed in this study. For each outcome (LR, DM and OS) performance of training and validation models, in terms of AUC and brier score were shown in table 1. Nomograms were generated for each outcome (LR, DM and OS) at 2, 3, 5 and 10 years. Furthermore as an example we have reported the new distant metastases nomogram at 5 years obtained (Figure 1).

Conclusion Despite its retrospective nature this analysis shows a significant impact of CRT dose on OS. This can explain the conflicting results of randomized trials on adjuvant CRT in PAC in which doses < 45 Gy were generally used. OC-0427 Prediction models in rectal cancer: an update of a pooled analysis of 3770 randomized patients V. Valentini 1 , C. Masciocchi 1 , J. Van Soest 2 , G. Chiloiro 1 , E. Meldolesi 1 , M. Gambacorta 1 , J. Gerard 3 , S. Ngan 4 , J. Bosset 5 , A. Sainato 6 , A. Damiani 1 , N. Dinapoli 1 , P. Lambin 2 , A. Dekker 2 , C. Roedel 7 1 Università Cattolica del Sacro Cuore -Policlinico A. Gemelli, Radiation Oncology Department, Rome, Italy 2 Maastricht University Medical Center, Radiation Oncology MAASTRO-GROW School for Oncology and Development Biology, Maastricht, The Netherlands 3 Unicancer- Centre Antoine Lacassagne, Radiotherapy, Nice, France 4 Peter MacCallum Cancer Centre, Division of Radiation Oncology, Melbourne, Australia 5 Besançon University Hospital J Minjoz, Radiation and Oncology, Besançon, France 6 Azienda ospedaliera Universitaria Pisana, Radiotherapy, Pisa, Italy 7 Goethe University Frankfurt, Radiotherapy and Oncology, Frankfurt am Main, Germany Purpose or Objective In the last years, several prognostic and predictive models (PMs) for locally advanced rectal cancer (LARC) patients (pts) have been developed. Aim of this study was to update the previous PMs [1] developed for local recurrence (LR), distant metastases (DM) and overall survival (OS) at 2, 3, 5 and 10 years based on a more copious pooled set of LARC pts. Material and Methods The PMs were developed using the data of the following LARC trials: Accord 12/0405, EORTC 22921, FFCD 9203, CAO/ARO/AIO-94, CAO-ARO-AIO-04, INTERACT, I-CNR-RT and TROG 01.04. Pts were selected applying the following exclusion criteria: neoadjuvant and adjuvant oxaliplatin based chemotherapy, no surgery procedure, short-course radiotherapy and no neoadjuvant radiotherapy. As the current pooled dataset contains different trials, we used 20% of the data (stratified per trial) as a validation dataset. Due to variable influence over time, a logistic regression model was used. Follow-up times (2, 3, 5 and 10 years) for the survival outcomes (LR, DM and OS) were used as the model outcome. Variable selection was performed using a stepwise Akaike's information criterion (AIC) feature selection to determine the optimal subset of

Conclusion The logistic regression models performed with AUC values always higher than 0.7. The AUC higher in validation than in training would need further investigation. Nomograms will be totally showed at the conference. [1] V. Valentini et al;Journal Clinical Oncology; 2011 [2] S. Gary et al; Research reporting method; 2015 OC-0428 Surgical time to increase pCR in rectal cancer: pooled set of 3078 patients from 7 randomized trials G. Chiloiro 1 , C. Masciocchi 1 , J. Van Soest 2 , E. Meldolesi 1 , M. Gambacorta 1 , J. Bosset 3 , J. Doyen 4 , J. Gerard 4 , S. Ngan 5 , C. Roedel 6 , F. Cellini 1 , A. Damiani 1 , N. Dinapoli 1 , P. Lambin 2 , A. Dekker 2 , V. Valentini 1 1 Università Cattolica del Sacro Cuore -Policlinico A. Gemelli, Radiation Oncology Department, Rome, Italy 2 Maastricht University Medical Center, Department of Radiation Oncology MAASTRO-GROW School for Oncology and Development Biology, Maastricht, The Netherlands