ESTRO 38 Abstract book

S32 ESTRO 38

estimated in a competing-risk framework. To account for bias consistent with non-random RT-assignment, propensity scores were estimated. Cox univariable analyses of association between RT and oncological endpoints was performed by applying inverse-probability- of-treatment-weight (IPTW) using propensity scores. Results Age, tumor size, and chemotherapy administration were significantly imbalanced between irradiated and unirradiated patients in all cohorts. IPTW removed all imbalances in key prognostic variables. The 8-year LR incidence in surgery + RT versus surgery only was 11.8% and 39.2% (p=0.011; WDLPS), 29.0% and 56.7% (p=0.008; grade I-II DDLPS), and 29.8% and 43.7% (p=0.025; grade III DDLPS), respectively, however this significant benefit was lost after IPTW-analyses. There we no significant differences in DM and OS between irradiated and unirradiated patients across all three cohorts. Conclusion Perioperative RT was associated with better LC on univariable unadjusted analyses in all cohorts, but not after accounting for imbalances in prognostic variables. RT did not impact on DM or OS. Appropriate selection of RT in this disease remains challenging. Results of the EORTC-STBSG 62092/22092 study are awaited. OC-0071 Stereotactic radiotherapy for nodal recurrences: an interim analysis from two phase I trials F. Deodato 1 , S. Cilla 2 , A. Ianiro 2 , V. Picardi 1 , M. Ferro 1 , M. Boccardi 1 , G. Tolento 3 , R. Cardano 3 , S. Cammelli 3 , P. Assalone 4 , M. Buwenge 3 , G.C. Mattiucci 5 , V. Valentini 5 , A.G. Morganti 3 , G. Macchia 1 1 Fondazione di Ricerca e Cura “Giovanni Paolo II”‐ Università Cattolica S. Cuore, Radiotherapy Unit, Campobasso, Italy; 2 Fondazione di Ricerca e Cura “Giovanni Paolo II”‐ Università Cattolica S. Cuore, Medical Physics Unit, Campobasso, Italy ; 3 Radiation Oncology Center, Dept. of Experimental‐ Diagnostic and Specialty Medicine – DIMES‐ University of Bologna‐ S.Orsola‐Malpighi Hospital, Bologna, Italy; 4 Veneziale Hospital, Oncology Unit, Isernia, Italy; 5 Policlinico Universitario “A. Gemelli”‐ Università Cattolica del Sacro Cuore, Department of Radiotherapy, Roma, Italy Purpose or Objective Stereotactic body radiotherapy (SBRT) has been shown to achieve high local control rates in limited metastatic burden of disease. Few papers reported on the efficacy of SBRT in limited nodal metastases. The primary aim was to review institutional outcomes of patients with solitary or oligometastatic lymph nodes treated with SBRT. Material and Methods Data from DESTROY-1 phase I and SRS-DESTROY-2 phase I clinical trials were reviewed and analyzed. These trials were a 5 fractions SBRT trial and a single fraction radiosurgery study, respectively (Figure 1). End-points were the detection of toxicities, overall response rate (ORR), and local control (LC). Tumor response was assessed according to the RECIST and EORTC PET criteria.Patients with all metastatic sites, primary tumor types and histologies were included between December 2003 and January 2018.

marginally resectable STS. It provides good pathological responses n advanced STS with acceptable treatment toxicity. OC-0070 Radiation Therapy for Retroperitoneal Liposarcoma – A report from TARPSWG R. Haas 1 , S. Bonvalot 2 , R. Miceli 3 , D. Strauss 4 , C. Swallow 5 , P. Hohenberger 6 , F. Van Coevorden 7 , P. Rutkowski 8 , D. Callegaro 9 , A. Hayes 4 , C. Honoré 10 , M. Fairweather 11 , R. Gladdy 5 , J. Jakob 6 , M. Szacht 8 , M. Fiore 9 , P. Chung 12 , W. Van Houdt 7 , C. Raut 11 , A. Gronchi 9 1 Netherlands Cancer Institute, Radiotherapy, Amsterdam, The Netherlands; 2 Institute Curie, Department of Surgery, Paris, France; 3 Fondazione IRCCS Istituto Nazionale dei Tumori, Unit of Clinical Epidemiology and Trial Organization, Milan, Italy ; 4 Royal Marsden Hospital NHS Foundation Trust, Department of Surgery, London, United Kingdom; 5 Mount Sinai Hospital and Princess Margaret Cancer Centre, Department of Surgical Oncology, Toronto, Canada ; 6 University Medical Center Mannheim‐ University of Heidelberg, Division of Surgical Oncology & Thoracic Surgery, Heidelberg, Germany; 7 Netherlands Cancer Institute, Department of Surgical Oncology, Amsterdam, The Netherlands; 8 Maria Sklodowska‐Curie Institute – Oncology Center, Department of Soft Tissue/Bone Sarcoma and Melanoma, Warsaw, Poland ; 9 Fondazione IRCCS Istituto Nazionale dei Tumori, Department of Surgery, Milan, Italy ; 10 Institute Gustave Roussy, Department of Surgery, Villejuif, France; 11 Brigham and Women’s Hospital and Center for Sarcoma and Bone Oncology‐ Dana‐Farber Cancer Institute‐ Harvard Medical School, Department of Surgery, Boston, USA ; 12 Mount Sinai Hospital and Princess Margaret Cancer Centre, Radiation Medicine Program, Toronto, Canada Purpose or Objective This study investigates the role of radiotherapy (RT) in patients with primary non-metastatic retroperitoneal liposarcomas.

Material and Methods 607 patients with localized retroperitoneal WDLPS and DDLPS were resected with or without RT at 8 high-volume sarcoma centers: 234 WDLPS, 242 GI-II DDLPS and 131 GIII DDLPS. RT was applied in 19.7%, 34.7% and 35.1% of these cohorts respectively. Overall survival (OS) was estimated by Kaplan-Meier method, and the incidences of local recurrence (LR) and distant metastasis (DM) were