ESTRO 2020 Abstract book

S656 ESTRO 2020

36% maintained this stage and 26% changed into T3a by SRMI. There were 8 patients with T2c by SCT, 37% changed into T3b. Only one patient was T4 and other was Tx with both tests.

performed in 264 patients, with a median follow-up of 35.6 months. Median pre-sRT PSA was 0.59ng/mL (IQR-0.763; 54.4% had >0.5ng/mL). Undetectable values were subsequently measured in 75 patients (28.4%), a median of 11.2 months after sRT (IQR-14.0). The group of patients who achieved undetectable PSA had a significantly shorter time from biochemical recurrence to sRT (6.6 versus 10.5 months in the detectable PSA group, p=0.025) and a lower rate of pre-sRT PSA >0.5ng/mL (37.3% versus 61.4% patients, p<0.001). There was also a higher rate of HT during sRT (9.3% versus 2.6%, p=0.042). All other relevant variables were balanced between the groups. Five patients in the undetectable PSA group later suffered a biochemical recurrence (6.7%), and two had a clinical recurrence (2.7%, distant). After undetectable PSA, a statistical significant improval was noted in BC-RFS, C-RFS, HT-FS and OS on univariate analysis (UVA). After multivariate analysis (MVA), the same effect was still observed in BC-RFS (92.8 versus 48.4% at 3 years; HR 0.135, CI95% 0.053-0.343, p<0.001 on MVA), C-RFS (98.0 versus 74.4% at 3 years; HR 0.106, CI95% 0.026-0.441, p=0.002 on MVA) and HT-FS (100 versus 71.5% at 3 years; HR 0.055, CI95% 0.007-0.406, p=0.004 on MVA). There was no significant effect on OS (possibly due to a low number of events - 100 versus 95.2% at 3 years, p=0.043 on UVA). Conclusion The achieval of undetectable PSA after sRT seems to be a predictor of less frequent biochemical and clinical recurrence. Hormone therapy-free survival and overall survival are also higher. An early sRT strategy (as soon as biochemical recurrence is diagnosed after radical prostatectomy, if possible before PSA reaches 0.5ng/mL), as currently recommended, could maximize the probability of undetectable PSA after sRT, and as such improve prognosis. PO-1156 The role of magnetic resonance imaging in prostate cancer E. González Del Portillo 1 , C. Gil Restrepo 1 , P. Soria Carreras 1 , M. Martín Izquierdo 2 , Á. Virseda Rodríguez 3 , J. García García 3 , F. Gómez Veiga 3 , L.A. Pérez Romasanta 1 1 Complejo Asistencial Universitario de Salamanca, Radiation Oncology, Salamanca, Spain ; 2 Complejo Asistencial Universitario de Salamanca, Radiology, Salamanca, Spain ; 3 Complejo Asistencial Universitario de Salamanca, Urology, Salamanca, Spain Purpose or Objective The local staging of prostate cancer (PC) is based on digital rectal examination (DRE) and conventional imaging strategies such as transrectal ultrasound (TUS) or computed tomography (CT). Today, multiparametric magnetic resonance imaging (mMRI) is increasingly used in order to improve tumor detection, local staging, prostate biopsy guidance and radiotherapy planning. Our goal is to assess the local staging (TNM 8th) with mMRI (SMRI) in comparison with the local staging achieved by conventional tests (SCT) in a group of patients with local disease. Material and Methods This is a retrospective study from 2017 to 2019. We collected data from 103 patients with localized PC. The SCT was based on DRE completed by a radiation oncologist or an urologist, plus TUS and CT. The SMRI employed MRI. Age, initial PSA (iPSA) and Gleason Score (GS) were registered. Results The median age was 69 years. The most frequent SCT was cT1cN0M0 (63%). In 67 patients we observed a change between SCT and SMRI (65%). The stages by both methods are included in Table 1. Out of the 66 patients with pT1c by SCT, 29% maintained the same stage and 32% changed into T2c by SRMI. Six patients were T2a with SCT and 66.6% did not change this stage with SMRI. Out of the 18 patients with T2b by SCT,

The percentage of patients who presented changes between SCT and SMRI according to the GS (6,7,8,9,10) and the iPSA ranges (<10, 10-20, >20 ng/ml) did not differ significantly (p 0.097 and p 0.057, respectively). We did not observe differences depending on the age (≤70 years vs. >70 years) between both staging methods (p 0.46). Twenty-three patients categorized as T1-T2 by SCT changed into T3 by SMRI. The median GS in this group was higher than in the group of patients without changes (7.92 vs. 6.83; p=0.000), with no differences regarding iPSA (18.49 ng/ml vs. 16.20 ng/ml; p=0.56). Conclusion The use of mMRI promotes changes in the local staging of the majority of our patients with localized PC. Patients categorized as T1-T2 by SCT who changed into T3 by SMRI presented higher GS. PO-1157 Short-term results of coverage probability radiotherapy of MRI-staged prostate cancer J. Marzec 1 , R. Eisenmann 1 , F. Paulsen 1 , D. Wegener 1 , B. Frey 1 , C. Zamboglou 2 , A. Othman 3 , K. Nikolaou 3 , M. Alber 4 , O. Dohm 5 , D. Thorwarth 6 , D. Zips 1 , A. Müller 1 1 University Hospital Tübingen, University Department of Radiation Oncology, Tübingen, Germany ; 2 University Medical Center Freiburg, Department of Radiation Oncology, Freiburg, Germany ; 3 University Hospital Tübingen, Department of Radiology, Tübingen, Germany ; 4 Ruprecht Karls University Heidelberg, University Department of RadioOncology and Radiotherapy, Heidelberg, Germany ; 5 University Hospital Tübingen, Medical Physics- University Department of Radiation Oncology, Tübingen, Germany ; 6 University Hospital Tübingen, Section for Biomedical Physics- University Department of Radiation Oncology, Tübingen, Germany Purpose or Objective We previously studied in a phase II trial the robustness of the coverage probability concept (CovP) for prostate cancer radiotherapy. Robust treatment planning led to very low G3+-toxicity and biochemical control of 95% after 7 years. Therefore, we evaluated this concept at our University Hospital in a larger patient cohort implementing magnetic resonance imaging (MRI)-based TNM-staging. Material and Methods