ESTRO 2025 - Abstract Book

S1590

Clinical – Mixed sites & palliation

ESTRO 2025

Material/Methods: Patients with locally advanced, non-curable superficial malignancies were considered for MBRT when conventional techniques were considered unlikely to achieve palliation without significant toxicity. MBRT was administered with the 180 kVp output of a clinical orthovoltage unit using 3-10 cm diameter cones treating lesions ranging in size from 2 to 20 cm. Peak dose was prescribed to skin surface or 1 cm depth, with valley doses dependent on peak dose and size of treatment cone. In- vivo dose was measured using radiochromic film placed on skin. Retrospective review of patient records was performed to assess treatment response and toxicity. Symptomatic and radiographic response were evaluated. Results: 21 patients with 28 treated lesions and mean age 65 were available for analysis; 13 patients had at least 3 months of follow-up. Pathology included squamous (n=7), melanoma (n=7), invasive ductal/lobular (n=3), colon adenocarcinoma (n=1), Merkel (n=1), serous ovarian (n=1), and liposarcoma (n=1). 15 (71%) had metastatic disease and 10 (48%) had recurrence at time of MBRT. 8 (38%) received prior RT with overlapping dose. Radiation peak doses and fractionation ranged from 10 Gy in 1 fraction to 90 Gy in 3 fractions; 30 Gy in 2 fractions was most commonly delivered. In all treatments, a clear delineation of peak and valley regions was evident from in vivo dosimetry. Sites of treatment included head and neck (n=17), trunk (n=10), and extremities (n=1). 8 patients (38%) received conformal EBRT as part of their radiotherapy. 16 (76%) patients received systemic therapy within 2 weeks of MBRT. 18 (86%) out of 21 patients had significant symptomatic relief from MBRT. Of patients with 3-month follow-up, 3 (23%) had radiographic disease reduction; 2 (15%) had complete radiographic response. 3 patients died due to cancer progression and 3 due to unrelated medical causes during follow-up. Overall, only 1 patient experienced G3 toxicity, a deep vein thrombosis related to a treated axillary mass considered possibly related to rapid tumor regression following treatment.

Conclusion: MBRT is an emerging therapy that may expand the armamentarium of radiotherapeutic options for bulky superficial tumors that are unlikely to be adequately treated with existing radiation modalities.

Keywords: Minibeam, Immunogenic, Spatially fractionated

4315

Digital Poster Re-irradiation with Proton therapy: acute toxicity and early clinical outcomes

Daniela Alterio 1 , Annamaria Ferrari 1 , Giulia Marvaso 1,2 , Gaia Piperno 1 , Maria Giulia Vincini 1 , Stefania Volpe 1,2 , Karl Amin 1,2 , Giancarlo Mazzola 1 , Luca Bergamaschi 1 , Federico Mastroleo 1 , Mattia Zaffaroni 1 , Federico Gagliardi 1 , Floriana Pansini 1 , Federica Cattani 1 , Marianna Alessandra Gerardi 1 , Marco Liotta 1 , Roberta Lazzari 1 , Roberto Orecchia 3 , Barbara Alicja Jereczek-Fossa 1 1 Division of Radiation Oncology, IEO, European institute of Oncology IRCCS, Milan, Italy. 2 Oncology and Hemato oncology, University of Milan, Milan, Italy. 3 Scientific directorate, IEO, European institute of Oncology IRCCS, Milan, Italy Purpose/Objective: Proton therapy (PT) represents a promising technique in the field of re-irradiation (reRT). Aim of this work was to report feasibility and early toxicity profile of patients treated with PT reRT at the Proton Center of the European Institue of Oncology, Milan, Italy.

Material/Methods: All consecutive patients (pts) treated with PT reRT between November 2023 and October 2024 were retrieved.