ESTRO 2025 - Abstract Book

S1806

Clinical – Upper GI

ESTRO 2025

References: [1] de Mol van Otterloo SR, Christodouleas JP, Blezer ELA, et al. (2020) The MOMENTUM Study: An International Registry for the Evidence-Based Introduction of MR-Guided Adaptive Therapy. Front Oncol. 10:1328. [2] Kroese SGC, Pavic M, Stellamans K, et al. (2023) Metastases-directed stereotactic body radiotherapy in combination with targeted therapy or immunotherapy: systematic review and consensus recommendations by the EORTC-ESTRO OligoCare consortium. Lancet Oncol. 24:e121-e132.

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Digital Poster MRI-Guided Stereotactic Body Radiation Therapy for oligometastatic splenic lesions - Initial experience. Lyndsey L Edwards Genesiscare, SJOG Hospital, Murdoch, Australia Purpose/Objective: Splenic metastasis is a rare occurrence which may be managed with splenectomy. However, this is associated with significant morbidity and infection risk [1]. Stereotactic body radiotherapy (SBRT) is commonly used to treat oligometastatic disease [2], but it's role for splenic metastasis is not well established. MR-guided radiotherapy (MRgRT)is particularly useful for moving intrabdominal organs such as the spleen to assist in reduction of treatment volume and enable the safe delivery of SBRT. Ongoing registries aim to create a repository of technical and clinical data to assist with the safe and effective delivery of MRgRT [3]. We report our mono-institutional experience of the safety and efficacy of splenic stereotactic MRgRT. Material/Methods: We prospectively collected data for four patients with oligometastatic splenic metastasis from our registry [3] who received MRgRT between February 2023 - October 2024. All patients were deemed unsuitable for surgery or local ablative treatment. Patients fasted 3 hours prior to both simulation and treatment. A 4DCT was obtained with patient immobilised in a vacuum bag, arms down and free breathing with a compression belt. Prescribed dose was 40 – 50Gy in 5 fractions delivered on non-consecutive days using the Adapt to Shape workflow. 3D vane sequence was utilised for target delineation to reduce motion artifacts. A uniform 5mm Planning Target Volume (PTV) expansion was applied depending on the target motion determined from the 4DCT. The spleen outline was used as a surrogate for motion monitoring on the 2D cine MRI. Full blood picture (FBP) was monitored before, during and after treatment. Response rates were determined based on CT or PET CT post-completion of MRgRT. Toxicities were recorded as per CTCAE version 5 criteria [4].

Results: Patient characteristics are outlined in Table 1. All patients completed treatment within 2.5 weeks.