ESTRO 2025 - Abstract Book

S1598

Clinical – Mixed sites & palliation

ESTRO 2025

With a median follow-up of 7.3 months (range 3.1-22.3 months), all patients were evaluated for acute toxicity with no occurrence of grade ≥ 3 SRS -related adverse events. Overall LC rate was 96.1%, with a 6- and 12-months freedom from local progression (LPFS) of 98.6% (95% CI 90.2-99.8) and 89.4% (95% CI 72.4-96.2), respectively. Tumor recurrence occurred in 15 (21.4%) patients, with a distant, regional, and mixed (local + distant) pattern as first site of failure in 10 (14.3%), 1 (1.4%), and 4 (5.7%) patients, respectively. After disease progression, 10 (14.3%) patients received a new line of systemic therapy (ST), 2 (2.9%) a combination of ST and palliative radiotherapy, while 3 (4.3%) patients a new course of stereotactic radiotherapy. One-year PFS, fNST, fPMD, and OS were 67.4% (95% CI 48.5 80.6), 72.4% (95% CI 52.8-85.0), 85.5% (95% CI 69.5-93.5), and 91.4% (95% CI 74.9-97.3), respectively. Conclusion: SRS is safe and effective, associated with high local control rate and excellent toxicity profile. After SRS, PFS and fNST appear promising in this oligometastatic population.

Keywords: oligometastases, radiosurgery, prospective study

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Digital Poster Hypofractionation in Proton therapy: the European Institute of Oncology preliminary experience Daniela Alterio 1 , Annamaria Ferrari 1 , Giulia Marvaso 1,2 , Gaia Piperno 1 , Stefania Volpe 1,2 , Maria Giulia Vincini 1 , Giovanni Carlo Mazzola 1 , Federico Mastroleo 1,2 , Roberta Lazzari 1 , Marianna Alessandra Gerardi 1 , Samantha Dicuonzo 1 , Floriana Pansini 1 , Mattia Zaffaroni 1 , Marco Liotta 1 , Federica Cattani 1 , Roberto Orecchia 1 , Barbara Alicja Jereczek-Fossa 1,2 1 Division of Radiation Oncology, IEO, European Institute of Oncology IRCCS, Milan, Italy. 2 Department of Oncology and Hemato-oncology, University of Milan, Milan, Italy Purpose/Objective: Hypofractionation (dose/fraction > 2Gy/fr) represents the standard of care for many tumors treated with photon based radiotherapy. Nevertheless, data on its use in the setting Proton therapy (PT) are still scares. Aim of this work