S1065
Clinical – Upper GI
ESTRO 2026
Purpose/Objective: Large hepatocellular carcinoma (HCC) remains a major challenge for radiotherapy due to limited hepatic reserve and the proximity of normal structures. Lattice Radiotherapy (LRT), a spatially fractionated technique, enables the delivery of ablative high-dose spheres within tumors while preserving organs at risk (OARs). We evaluated the feasibility, early response, and safety profile of VMAT-based LRT for large HCC. Material/Methods: We retrospectively reviewed seven patients (eight LRT courses) with large unresectable HCC or extrahepatic metastatic lesions treated between October 2024 and August 2025. Patients included had Child-Pugh A or B liver function and lesions greater than 400 cm ³ . All had received prior locoregional or systemic therapies— HAIC, TAE, or atezolizumab/bevacizumab—with five continuing immunotherapy during or after radiotherapy. Each plan incorporated 8–24 high-dose spheres (18–20 Gy, single fraction), combined with peripheral doses ranging from 20 to 52.5 Gy in 5–15 fractions. Treatment planning aimed to spare the normal liver and OARs. Outcomes included treatment feasibility, acute and late toxicities (CTCAE v4.0), and radiographic response at 3 months. Results: The median follow-up was 6 months. In this cohort, most patients were BCLC stage C. The median age was 72 years (range, 50–93 years), and tumor volumes ranged from 422 to 2150 cm ³ . Each plan incorporated 8–24 high-dose spheres (the most commonly delivered dose to spheres was 20 Gy in a single fraction), combined with peripheral doses (the most common peripheral dose was 37.5 Gy in 15 fractions). The median mean liver dose was 13 Gy (range, 1.95–17.13 Gy). Five patients received concurrent and maintenance therapy with atezolizumab/bevacizumab. One patient underwent a second LRT course for residual tumor. Acute toxicity was limited to Grade 0– 2. At three months post-treatment, no evaluable patients exhibited radiation-induced liver disease above Grade 0 or experienced other late toxicities. Three months following LRT, the median tumor volume decreased by 55% (to 333 cm ³ ). Two patients converted from partial to complete response during the follow-up period. Notably, rapid tumor regression was observed during the first 1 to 3 fractions in two cases, accompanied by prompt symptomatic relief.
Conclusion: VMAT-based Lattice Radiotherapy is a feasible, OAR- sparing approach for large HCC, enabling aggressive intratumoral dosing without compromising hepatic function. The early and durable tumor regression, combined with preserved systemic therapy, suggests potential for immune-mediated synergy. Further prospective studies are warranted to validate LRT as an immuno-priming platform in the treatment of large HCC. Keywords: Lattice radiotherapy, HCC, immunogenic modulation Personalizing oesophageal cancer therapy: A validated multicentre model to stratify 2-year mortality in patients receiving neoadjuvant chemoradiation. Mark L. Frederiks 1 , Rob H.A. Verhoeven 2,3 , Ewoud Schuit 4 , Peter S.N. van Rossum 5 , Gert J. Meijer 6 , Stella Mook 6 , Joost J. Nuyttens 7 , Heidi Rütten 8 , Bastiaan R. Klarenbeek 9 , Mariska D. den Hartogh 10 , Meindert Sosef 11 , Boudewijn van Etten 12 , Bas P.L. Wijnhoven 13 , Hanneke W.M. van Laarhoven 14 , Johannes A. Langendijk 1 , Maaike Berbée 15 , Christina T. Muijs 1 1 Department of Radiation Oncology, University Medical Center Groningen, Groningen, Netherlands. 2 Department of Research & Development, Poster Discussion 736 Netherlands Comprehensive Cancer Organisation (IKNL), Utrecht, Netherlands. 3 Department of Medical Oncology, Cancer Center Amsterdam, Amsterdam, Netherlands. 4 Department of Epidemiology & Health Economics, Julius Center for Health Sciences and Primary Care, Utrecht, Netherlands. 5 Department of Radiation Oncology, Amsterdam UMC, Amsterdam, Netherlands. 6 Department of Radiation Oncology,
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