S918
Clinical - Mixed sites & palliation
ESTRO 2026
melanoma (15%). Median DS-GPA was 2,9 (1-4). Median KPS was 85% (60-100). All patients except one were oligometastatic. Surgery was complete in all cases. All patients received 15,40 Gy with a median surface dose of 22,34 Gy (20,06-24,2) in a median time of 16,25 minutes (7,40-39,29). Treatment administration was interrupted during 5 minuts in one patient due to a tendency to hypertension. One patient with thrombocytopenia presented intra and postoperative cerebral bleeding. Another patient presented an asymptomatic distal jugular and lateral sinus thrombosis. Median hospitalization time was 5,6 days.After a minimum follow-up of 33 months, 4 patients died prematurely from sepsis, peritonitis, rapid brain tumour progression and thrombocytopenia with fatal cerebral bleeding. Regional (brain) progression of the remaining 16 patients was 43,8% including 1 nodular leptomeningeal disease 6 month after surgery. Many patients receive new local treatments with SRS or FSRT; 2 patients were treated with salvage WBRT. Local control at 33 months was 92% with only one local relapse at 8 months after surgery. We noted only one symptomatic radiation necrosis in a patient previously locally treated by FSRT. Conclusion: IORT appears as a highly effective option to ensure local control after surgery of brain metastases with minimal risk of complications. The two procedures performed at a single time would allow the rapid initiation of systemic therapy if indicated. Keywords: BRAIN METASTASES, INTRAOPERATIVE RADIOTHERAPY, Feasibility and efficacy of re-irradiation with magnetic-resonance-image guided radiation therapy (MR- LINAC) Lucas Mose 1 , Inga Jessen 1 , Lars Wessel 1 , Fabian Allmendinger 1 , Maximilian Deng 1 , Brügemann Dirk 1 , Schlüter Fabian 1 , Katharina Renkamp 1 , Regnery Sebastian 1 , Klüter Sebastian 1 , Juliane Hörner-Rieber 2 , Laila König 1 , Jürgen Debus 1 , Jakob Liermann 1 , Philipp Hoegen-Saßmannshausen 1 1 Department of Radiation Oncology, Heidelberg University, Heidelberg, Germany. 2 Department of Radiation Oncology, University Hospital Düsseldorf, Düsseldorf, Germany Purpose/Objective: Recently, the use of re-irradiation has rapidly increased. Achieving an optimal balance between minimizing radiation toxicity and maximizing local Digital Poster 4482
Poster Discussion 4477 Second interim analysis of the phase II trial of intraoperative radiotherapy with INTRABEAM after surgical resection of brain metastases (NCT05084092) Miquel Maciá 1 , Anna Lucas 2 , Nagore G Expósito 1 , Aleix Rosselló 3 , Alejandro F Coello 3 , Pere Josep Cifre 3 , Noemi Vidal 4 , Carles Majós 5 , Albert Pons 5 , Montse Ventura 1 , Pablo Saldaña 6 , Gerard Plans 3 1 Radiation Oncology, Institut Catalá d'Oncologia, Hospitalet de LlobregatBarcelona, Spain. 2 Radiation Oncology, Institut Catalá d'Oncologia, Hospitalet de Llobregat, Spain. 3 Neurosurgery, Hospital de Bellvitge, Hospitalet de Llobregat, Spain. 4 Patology, Hospital de Bellvitge, Hospitalet de Llobregat, Spain. 5 Institut Diagnóstic per la Imtage, Hospital Duran i Reynals, Hospitalet de Llobregat, Spain. 6 Medical Physics, Institut Catalá d'Oncologia, Hospitalet de Llobregat, Spain Purpose/Objective: WBRT has been replaced for different types of focal irradiation: radiosurgery or hypofractionated stereotactic radiotherapy to improve local control after surgical resection of brain metastases (BM). Intraoperative Radiotherapy (IORT) involves delivering a single, high dose of radiation directly to the tumor bed during surgery offering several advantages: precise targeting of tumor bed, potentially reduction of radiation-related complications, avoidance of tumor repopulation before external postoperative RT and rapid initiation of systemic treatment if indicated. Material/Methods: Inclusion criteria for phase II trial: KPS ≥ 70%, complete resection of BM, peroperative histological confirmation, no dural attachment and adequate distance to optic apparatus and brainstem. Previous RT was not an absolute exclusion criterion. After en bloc resection, administration of a fixed dose of 15,40 Gy prescribed at 2 mm depth with INTRABEAM (X-ray 50 Kv) using the appropriated sized applicator was planned. Primary endpoint was local (cavity + 5 mm) progression free survival. Results: Median age of the first 20 analyzable patients was 58,8 years (40-78). Lung cancer was the most frequent primary tumour (55%), followed by breast (15%) and
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