ESTRO 2021 Abstract Book

S1141

ESTRO 2021

translational axes. The deviation over time in the group of primary treated patients was significantly larger than that of the group of patients who were re-irradiated, leading to a mean deviation of 2.73 (sd=1.00) versus 1.90 (sd=0.79), p<0.001. Conclusion This is the first study to focus on intra-fraction prostate motion in the context of re-irradiation. We observed that intra-fraction prostate motions persisted in the setting of re-irradiation although they were significantly reduced compared to first irradiation. These results will help to better estimate random error during the SBRT treatment of an intra-prostatic recurrence after irradiation. PO-1391 Curative 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 , 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 the outcome of prostate cancer patients treated with curative radiotherapy based on a comprehensive analysis of tumor, patients, and treatment characteristics. Furthermore, we aimed to develop a simple risk stratification system based on real life data from a large patients’ population. Materials and Methods A retrospective analysis of 1074 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 At multivariate analysis, a worse bRFS was observed in patients with: higher PSA levels, higher Gleason Score (GS) values, and wider margins between CTV and PTV. A lower LC rate was observed in patients with higher GS, and with a larger CTV to PTV margin, while higher values were recorded in patients treated with adjuvant androgen deprivation therapy (ADT) or with a Charlson’s comorbidity index > 1. DFS was lower in patients with larger margins between CTV and PTV, while a higher DFS was recorded in patients undergoing TURP or adjuvant ADT. However, a worse MFS and DFS was recorded in patients with higher GS values. OS correlated only with the presence of a GTV to CTV margin. In fact, patients planned with this margin showed an improved OS. We designed a prognostic model of 5-year bRFS using three PSA categories and five GS categories to define 15 different groups of patients. We arranged these 15 group in only four categories based on the 5-year bRFS values: group 1: very low-risk (bRFS > 90%), group 2: low risk (bRFS: 80-90%), group 3: intermediate risk (bRFS: 60-79.9%), group 4: high risk (bRFS < 60%) [ Figure 1 ]. Conclusion This systematic analysis of a large database allowed identifying unforeseen correlations that can generate new hypotheses. These results justify further analysis on large series of patients with prostate cancer treated with curative radiotherapy, possibly performed with more advanced statistical analysis methods. model. Results