ESTRO 2025 - Abstract Book

S1579

Clinical – Mixed sites & palliation

ESTRO 2025

4201

Digital Poster Reirradiation of Bone Metastases: Satisfactory Local Control with Low Toxicity in a Large Retrospective Series Ilaria Repetti 1,2 , Chiara Lorubbio 1,2 , Federico Mastroleo 1,2 , Maria Giulia Vincini 1 , Mattia Zaffaroni 1 , Costantino Putzu 1,2 , Cristiana Iuliana Fodor 1 , Annamaria Ferrari 1 , Gaia Piperno 1 , Daniela Alterio 1 , Elena Rondi 1 , Stefania Comi 1 , Floriana Pansini 1 , Francesca Emiro 1 , Giulia Marvaso 1,2 , Barbara Alicja Jereczek-Fossa 1,2 1 Division of Radiation Oncology, European Institute of Oncology, Milan, Italy. 2 Department of Oncology and Hemato oncology, University of Milan, Milan, Italy Purpose/Objective: Longer survival of metastatic patients (pts) has resulted in increased demand for second course of radiation therapy (reRT) in pts with previously irradiated bone metastases. In this context, high-quality evidence on which reRT schemes or techniques to use, is lacking. Aim of the present study is to evaluate efficacy and safety of reRT in pts with previously irradiated bone metastases. Material/Methods: Data of pts who underwent reRT on bone metastases at European Institute of Oncology, from December 2011 to May 2024 were retrospectively considered for study inclusion. Both type 1 and type 2 reRT were allowed(1). The primary endpoint was local control (LC). Time to local failure was calculated from the end of reRT treatment to the date of local progression assesed by radiological imaging. Secondary endpoints were acute and late toxicities and overall survival (OS). For every reRT treatment a dosimetric evaluation of the previous radiotherapy (RT) plan, when available, was done, taking into consideration the Equivalent Dose in 2Gy Fractions (EqD2) at organs at risk (OARs). For lesions close to spinal cord and cauda equina, BED dose of first and reRT was calculated following Nieder at al. indications (2). When the previous RT plan was not available the worse case scenario was considered. Toxicities were assessed according to RTOG/EORTC scale. Results: A total of 159 pts were included. Pts and treatment characteristics are listed in Table 1 . Most reRT were type 1 according to ESTRO/EORTC classification. Median reRT total EqD 2 (α/β=3) was 28 Gy (IQR 24 – 40). Median time between the first RT and reRT was 20.8 months (IQR 12.3 – 38.5). At a median follow-up time of 18.7 months (IQR 9.7 – 34.2, FUP available for 137), 69 bone lesions progressed after reRT with a median time to local failure of 7.9 months (IQR 3.3 – 10.6). LC rate at 1 year was 58% (available for 106 pts). Toxicities are reported in Table 2 . After reRT 13 cases of vertebral collapse or bone fracture were registered. No acute and late toxicities greater than G1 were registered except for one patient who experienced acute brachial plexopaty (G2) and one patient who experienced late spinal cord compression (G3). At last contat 88 pts were alive with desease (64.2%) while 49 pts were dead (35.8%).