ESTRO 38 Abstract book

S838 ESTRO 38

patients and in favorable-intermediate risk, 18.2% and 35.5% patients after mpMR upgrade to T3, respectively. We observe that among GG1 patients, 14 % and GG2 45.5% increased their stage. In patients with PSA <10ng/ml,13.3% had an increase in stage. Between patients with PSA >10ng/ml, 23% upgrade to T3 after mpMR.

Purpose or Objective To investigate the impact of magnetic resonance imaging (MRI) information on clinical staging, risk stratification and treatment recommendations for prostate cancer (PCa) according to the European Association of Urology (EAU) guidelines. Material and Methods We performed a single-centre analysis of 180 men with PCa, undergoing clinical staging by digital rectal examination (DRE) as well as MRI before their robot- assisted radical prostatectomy between April 2016 and December 2017. Patients were stratified according to the EAU guidelines based on their clinical T-stage assessed by either DRE or MRI, initial prostate specific antigen (iPSA) value and Gleason score. Furthermore, to combine the best of both world, we created a combined clinical T-stage definition and investigated its accuracy. This combined clinical T-stage takes into account the DRE-based clinical staging for peripheral zone tumours, except for anterior located tumours not detected by DRE (cT1c). In this case, as well as for tumours with a transitional zone tumour component, the combined clinical T-stage is determined by MRI-based clinical T-staging. Differences in risk classification and recommended optimal duration of concomitant androgen deprivation therapy (ADT) between DRE- and MRI-staging were analysed using a paired- samples sign test. In all analysis of differences, a statistical significance level of p<0.05 was used. Results Use of MRI information instead of DRE information leads to significant upstaging of clinical T-stage (33%) and EAU risk grouping (31%). When comparing these results with the pT- stage after histopathological evaluation, MRI showed a significantly higher sensitivity than DRE to detect non- organ-confined PCa (59% vs. 41%; p<0.01). In contrast the specificity of MRI was significantly worse than DRE (69% vs. 95%; p<0.01). The combined clinical T-stage approach (DRE-MRI) showed a sensitivity of 58% and a specificity of 79% to detect non-organ-confined PCa. Incorporation of MRI only information in the treatment decision process based on the EAU guidelines would alter the choice of surgical treatment in 49/180 patients (27%) with in most cases less nerve-sparing surgery (46/180 patients (26 %)). When we focus on radiation treatment with concomitant ADT, the treatment would be intensified in 46/180 patients (26%) with ADT prolongation as a result of upstaging by MRI. When the combined clinical T-stage approach (DRE-MRI) would be used, treatment would be intensified in 36/180 patients (20%). Conclusion The incorporation of MRI information substantially affects the treatment choice in PCa patients as compared to using the current available EAU guidelines based on DRE information. More specifically, treatment intensification would be recommended in 1 out of 4 patients. Hence, there is a clear need for contemporary, updated MRI- based stratification tools and treatment guidelines to avoid overtreatment. Currently, a combined DRE-MRI- based assesment could be a pragmatic approach for cT- staging of PCa tumours. EP-1553 High-dose hypofractionated helical IG-IMRT in high-risk prostate cancer patients N.G. Di Muzio 1 , C.L. Deantoni 1 , F. Zerbetto 1 , C. Cozzarini 1 , S. Broggi 2 , P. Mangili 2 , A. Chiara 1 , I. Dell'Oca 1 , A.M. Deli 1 , R. Calandrino 2 , C. Fiorino 2 , A. Fodor 1 1 San Raffaele Scientific Institute, Department of Radiotherapy, Milan, Italy ; 2 San Raffaele Scientific Institute, Medical Physics, Milan, Italy Purpose or Objective Recently Kishan and co-workers (JAMA 2018) demonstrated that high-risk prostate cancer patients treated with dose-escalated external beam radiotherapy and more than 24 months of androgen deprivation have

Conclusion According to the results obtained, we observed that 25% of patients diagnosed of localized prostate cancer with low-intermediate risk upgrade T stage after MRI. Switching to T3 stage of any type after MRI is more frequent in Grade 2 patients and favorable-intermediate risk groups. Grouping extended T3a and T3b we obtain 15.52.% (n=9). This percentage of more extended occult disease is close to historically reported recurrence (15- 25%).That is, with high reliability 15% of low- risk patients upgrade to high- risk groups. Without MRI, these patients could be under- treated according to a poor initial stage with the usual methods, which could be the cause of recurrence and subsequent metastasis. EP-1552 Impact of MRI on prostate cancer risk classification: game changer for therapeutic decision making? C. Draulans 1,2 , W. Everaerts 3,4 , S. Isebaert 1,2 , G. Thomas 4 , R. Oyen 5,6 , S. Joniau 3,4 , E. Lerut 6,7 , L. De Wever 5 , B. Weynand 6,7 , E. Vanhoutte 5 , G. De Meerleer 1,2 , K. Haustermans 1,2 1 University Hospitals Leuven, Department of Radiation Oncology, Leuven, Belgium ; 2 KU Leuven, Department of Oncology, Leuven, Belgium ; 3 University Hospitals Leuven, Department of Urology, Leuven, Belgium ; 4 KU Leuven, Department of Development and Regeneration, Leuven, Belgium ; 5 University Hospitals Leuven, Department of Radiology, Leuven, Belgium ; 6 KU Leuven, Department of Imaging and Pathology, Leuven, Belgium ; 7 University Hospitals Leuven, Department of Histopathology, Leuven, Belgium