ESTRO 2021 Abstract Book

S683

ESTRO 2021

recorded. And there were procedure related Hemoperitoneum resulted from fiducial marker insertion(n=1). Additionally, Cyberknife synchrony tumor tracking log file was analyzed. intrafractional movement in terms of overall correlation error were -0.3±1.3, 0.0±0.6, -0.2±0.6 for CC, LR, and AP axis, respectively. Conclusion This preliminary results show that CK for primary RCC was feasible and also well tolerated. with high rate of local control and functional preservation. PD-0849 Concomitant Nivolumab and RT in metastatic kidney cancer. Benefit of ablative vs palliative approach G. Francolini 1 , V. Di Cataldo 2 , B. Detti 1 , M. Loi 1 , P. Ghirardelli 3 , V. Vavassori 3 , L. Nicosia 4 , F. Alongi 4 , L. Triggiani 5 , S. La Mattina 5 , A.G. Allegra 6 , E. Scoccimarro 6 , M. Aquilano 6 , S. Lucidi 6 , M. Valzano 6 , A. Peruzzi 7 , I. Morelli 6 , M. Mariotti 6 , V. Salvestrini 6 , G. Stocchi 6 , L.P. Ciccone 6 , I. Desideri 6 , L. Livi 6 1 Azienda Ospedaliera Universitaria Careggi, Radiotherapy Unit, Florence, Italy; 2 Istituto Fiorentino di Cura e Assistenza (IFCA), Radiotherapy Unit, Florence, Italy; 3 Cliniche Humanitas Gavazzeni, Department of Radiotherapy, Bergamo, Italy; 4 IRCCS Sacro Cuore Don Calabria Hospital, Negrar, Radiation Oncology, Verona, Italy; 5 University and Spedali Civili Hospital, Department of Radiation Oncology, Brescia, Italy; 6 University of Florence, Department of Experimental and Clinical Biomedical Sciences "M. Serio", Florence, Italy; 7 Unviersity of Florence, Department of Experimental and Clinical Biomedical Sciences "M. Serio", Florence, Italy Purpose or Objective Immune checkpoint inhibition (ICI) with Nivolumab has become one of the treatment cornerstone for treatment of metastatic renal cell carcinoma (RCC) both in first and second line setting. Biological rationale for the additive effect of stereotactic body radiotherapy (SBRT) and ICI is based on multiple pre-clinical evidences, yet clinical evidence of a synergistic effect between SBRT and Nivolumab is still lacking, after NIVES trial failed to meet its primary endpoint. To explore the benefit of SBRT if compared to palliative only RT in addition to ICI, we present a multicentric retrospective series of patients treated with concomitant RT and Nivolumab for metastatic RCC. Materials and Methods Data about 40 patients undergoing Nivolumab therapy and treated on 52 metastatic lesions were retrospectively reviewed and collected. Treatment were considered concomitant if administered within < 4 months (either RT before Nivolumab or reverse sequencing). RT was defined Ablative if > 5 Gy per fraction were administered. Both patients undergoing ICI in I and II line were included in the current analysis. Overall survival (OS) was defined as time between Nivolumab Start and death, Progression-free survival (PFS) was defined as time between Nivolumab start and end. Results After a median follow-up of 11 months (IQR 4.7-17.6), 16 patients died. Overall median PFS and OS were 6 months (95% CI 5-10) and 24 months (95% CI 13-24), respectively. Local progression occurred in 14 treated lesions (26.9%), 5 and 9 in the ablative and palliative RT group, respectively. Distant progression was reported after treatment of 39 lesions (75%), 19 and 20 in the ablative and palliative RT group, respectively. At univariate analysis, median PFS was significantly associated to absence of metastasis at diagnosis (9 vs 4 months, p=0.005) and ablative RT intent (20 vs 5 months, p<0.0001). Median OS was also improved in patiens without evidence of metastatic disease at diagnosis (not reached vs 11 months, p=0.02) and treated with concomitant ablative RT (not reached vs 11 months , p=0.001). At multivariate analysis, RT ablative intent was confirmed as the only independent prognostic factor significantly associated with PFS ( HR 3.51, 95% CI 1.6- 7.5, p=0.0012) and OS (HR 2.8, 95% CI 0.99-8.07, p=0.05). > G2 adverse events were reported in 14 patients (7 endocrine, 2 skin rash, 1 pneumonitis, 3 hepatic, 2 pancreatic). Conclusion RT administered with ablative intent had a significant impact on survival of patients treated with concomitant Nivolumab if compared to patients undergoing palliative-only treatment. Toxicity of the concomitant treatment was mild and mainly related to Nivolumab treatment. These encouraging results prompt to explore this combination strategy in prospective trials. PD-0850 Adjuvant radiotherapy after cystectomy for patients with bladder cancer: a phase II trial. V. Fonteyne 1 , P. Dirix 2 , C. Van Praet 3 , C. Berghen 4 , M. Albersen 5 , S. Junius 6 , N. Liefhooghe 7 , L. Noé 8 , G. De Meerleer 4 , P. Ost 9 , K. Decaestecker 10 1 Ghent University Hospital, Radiotherapy-Oncology, Ghent, Belgium; 2 iridium Cancer Network, Radiotherapy- Oncology, Antwerp, Belgium; 3 Ghent University Hospital, urology, Ghent, Belgium; 4 University Hospitals Leuven, Radiotherapy-Oncology, Leuven, Belgium; 5 University Hospitals Leuven, Urology, Leuven, Belgium; 6 CH-M/AMPR, Radiotherapy-Oncology, Mouscron, Belgium; 7 AZ Groeninge , Radiotherapie-Oncologie, Kortrijk, Belgium; 8 Limburg Oncology Centre, Radiotherapy-Oncology, Hasselt, Belgium; 9 Ghent University, Department of Human structure and Repair, Ghent, Belgium; 10 Ghent University Hospital, Urology, Ghent, Belgium Purpose or Objective Neo-adjuvant chemotherapy (NAC) followed by a radical cystectomy (RC) with extended pelvic lymph node dissection (ePLND) is considered to be the golden standard for patients with muscle invasive bladder cancer (MIBC). Despite this multimodality treatment, the outcome is poor and ultimately 30% of the patients with ≥pT3 tumors will develop a pelvic recurrence (1). Five-year MIBC-specific survival is only 48 and 31% for T3 and T4 MIBC patients respectively (2). Adjuvant external beam radiotherapy (EBRT) was tested in a prospective randomized trial, and resulted in a 20% increase in 5-year disease-free survival (DFS) (3). Adjuvant EBRT might thus prevent loco-regional recurrence and improve DFS and overall survival. Despite those encouraging results, severe intestinal toxicity rates hampered the adoption of adjuvant EBRT (3). We examined whether adjuvant pelvic EBRT with intensity