ESTRO 2025 - Abstract Book

S785

Clinical - Gynaecology

ESTRO 2025

Agostino Gemelli IRCCS, Roma, Italy. 3 Department of Radiation Oncology, IRCCS San Raffaele Scientific Institute, Milano, Italy. 4 Radiotherapy Unit, Ospedale "Vito Fazzi", Lecce, Italy. 5 UOC Radiotherapy, Nuovo Ospedale degli Infermi, Biella, Italy. 6 Radiation Oncology Center, S Maria Hospital, Terni, Italy. 7 Radiotherapy and Radiosurgery Department, Humanitas Clinical and Research Center-IRCCS, Milano, Italy. 8 U.O.C. di Radioterapia, Azienda Ospedaliera “Cannizzaro”, Catania, Italy. 9 Radiation Oncology, Azienda USL – IRCCS di Reggio Emilia, Reggio Emilia, Italy. 10 Medical Oncology Unit, Responsible Research Hospital, Campobasso, Italy. 11 Research Laboratories, Responsible Research Hospital, Campobasso, Italy. 12 Medical Physics Unit, Responsible Research Hospital, Campobasso, Italy. 13 Radiation Oncology, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy. 14 Department of Medical and Surgical Sciences (DIMEC), Alma Mater Studiorum-Bologna University, Bologna, Italy. 15 Istituto di Radiologia, Università Cattolica del Sacro Cuore, Roma, Italy. 16 UOC Ginecologia Oncologica, Dipartimento Scienze della Salute della Donna e del Bambino, Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Roma, Italy. 17 Oncologia Clinica Sperimentale Uroginecologica, Istituto Nazionale Tumori IRCCS Fondazione G. Pascale, Napoli, Italy Purpose/Objective: The results of stereotactic body radiotherapy (SBRT) for parenchymal lesions, in the setting of oligometastatic ovarian cancer (oligo-MPR-OC) are reported in the context of the prospective multicenter Phase II MITO-RT3/RAD trial (NCT04593381) [1]. Material/Methods: The primary endpoint was the complete response (CR) rate, secondary endpoints included local control (LC), progression-free survival (PFS), overall survival (OS), treatment-free interval (TFI), and toxicity rates. Sample size was based on a previous study reporting an average 40.0% CR with SBRT. The study was powered to detect an improvement in the CR rate from 40.0% to 55.0%, with an α error of 0.05 (one-side) and a β error of 0.1. Results: The study met its primary endpoint of a statistically significant improvement of CR. 88 patients with 127 lesions were enrolled across fifteen Institutions from November 2020 to January 2024. CR was observed in 71 lesions (55.9%), PR in 37 (29.1%), SD in 14 (11.0%), and Progressive Disease (PD) in five lesions (4.0%). The ORR was 85.0%, with an overall clinical benefit rate of 96.0%. The overall 12-month LC was 81.6%, with CR lesions exhibiting a significantly higher rate than partial or not responding lesions (12-month LC: 96.3% vs. 61.4%, p<0.001). The 12-month actuarial rates for PFS and OS were 34.9% and 91.5%, respectively. The median actuarial TFI was 9 months (range 2.5-15.4 months), while the 12-month actuarial rate was 44.1%. No toxicity > Grade 3 was reported. In particular, 15 (20.5%) patients experienced mild acute toxicity (≤ Grade 2). There were 12 Grade 1 events and 6 Grade 2 events, the latter mostly represented by pain flare (N=2). Late toxicity was reported in 4 patients (4.5%) accounting for 4 events, mostly Grade 1, except for one case of moderate asthenia (Grade 2). Conclusion: The MITO-RT3/RAD trial showed a high rate of complete response and encouraging long-term outcomes for patients achieving CR, including a substantial period of systemic therapy-free survival after radiotherapy. The observed toxicity was minimal, strengthening the safety of SBRT for oligo-MRP-OC ablation as a non-invasive alternative to surgical resection for parenchymal metastases in high-risk areas.

Keywords: Ovarian Cancer; SBRT; Parenchymal Lesions

References: 1. Macchia G, Jereczek-Fossa BA, Lazzari R, Cerrotta A, Deodato F, Ippolito E, Aristei C, Gambacorta MA, Scambia G, Valentini V, Ferrandina G. Efficacy and safety of stereotactic body radiotherapy (SBRT) in oligometastatic/persistent/recurrent ovarian cancer: a prospective, multicenter phase II study (MITO-RT3/RAD). Int J Gynecol Cancer. 2022 Jul 4;32(7):939-943.