ESTRO 2021 Abstract Book

S1142

ESTRO 2021

PO-1392 Salvage radiotherapy of prostate cancer: a risk stratification system based on prognostic factors S. Bisello 1,2 , A. Arcelli 1,2 , F. Deodato 3,4 , N. Dominsky 2 , G. Tarantino 2,5 , M. Ntreta 1 , S. Cilla 6 , G. Siepe 1 , L. Cavallini 1,2 , D. Pezzulla 3 , A.R. Alitto 7,8 , A. Re 3 , S. Cammelli 1,2 , A. Cortesi 9 , A. Romeo 9 , G.P. Frezza 10 , A.G. Morganti 1,2 , G. Macchia 3 , M. Buwenge 1,2 1 Radiation Oncology, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy; 2 Department of Experimental, Diagnostic, and Specialty Medicine - DIMES, Alma Mater Studiorum Bologna University, Bologna, Italy; 3 Radiation Oncology Unit, Gemelli Molise Hospital – Università Cattolica del Sacro Cuore, Campobasso, Italy; 4 Istituto di Radiologia, Università Cattolica del Sacro Cuore, Roma, Italy; 5 Dana Farber Cancer Institute, Harvard Medical School, Boston, MA, USA; 6 Medical Physics Unit, Gemelli Molise Hospital – Università Cattolica del Sacro Cuore, Campobasso, Italy; 7 Istituto di Radiologia, Università Cattolica del Sacro Cuore, Roma, Italy; 8 Fondazione Policlinico Universitario A. Gemelli, IRCCS, UOC di Radioterapia, Dipartimento di Scienze Radiologiche, Radioterapiche ed Ematologiche, Roma, Italy; 9 Radiotherapy Unit, IRCCS Istituto Romagnolo per lo Studio dei Tumori (IRST) "Dino Amadori", Meldola, Italy; 10 Radiotherapy Department, Ospedale Bellaria, Bologna, Italy Purpose or Objective The aim of this study was to analyse the prognostic impact on outcome of prostate cancer patients treated with salvage radiotherapy based on a comprehensive analysis of tumor, patients, and treatment characteristics. Furthermore, our aim was to develop a simple risk stratification system based on real life data from a large patients’ population. Materials and Methods A retrospective analysis of 454 patients enrolled in an observational study was performed. Endpoints of the study were biochemical relapse-free survival (bRFS), local control (LC), regional control (RC), metastasis-free survival (MFS), disease-free survival (DFS), and overall survival (OS). Variables with P value less than 0.05 or with a trend (p < 0.1) at univariate analysis (log rank) were entered into a multivariate Cox’s regression stage, lower Gleason score (GS) and treated with prophylactic nodal irradiation (PNI). Moreover, it showed an improved LC in patients treated with hypofractionated regimens. In terms of RC, better results in patients with lower GS and worse results in patients with negative surgical margins, treated with IMRT/VMAT technique, and not receiving PNI were observed. The analysis on MFS showed a better outcome in pN 0 and low GS patients and a higher failure risk in patients receiving adjuvant androgen deprivation therapy . Higher DFS rates were confirmed in patients with pN 0 or low GS or low PSA levels at salvage treatment as well as in patients treated with Cone-Beam CT. Furthermore, better DFS rates in patients receiving PNI were recorded. OS rates were higher with IMRT/VMAT techniques. We designed a prognostic model using four GS categories, two nodal stage categories, and two nodal irradiation categories to define 16 different groups of patients. These 16 groups were arranged in only model. Results Multivariate analysis showed higher bRFS rates in patients with pN 0