ESTRO 2025 - Abstract Book

S1459

Clinical – Mixed sites & palliation

ESTRO 2025

Conclusion: Proton therapy offers potential for reducing toxicity and improving survival outcomes in selected malignancies. s. Ongoing research is essential to further define its role across different tumour types.

Keywords: Proton beam therapy, systematic review, trials

References: 1. Liao et al. Journal of Clinical Oncology. 2018 2. Lin et al. Journal of Clinical Oncology. 2020 3. Brown et al. Neuro-Oncology. 2021 4. Mohan et al. Neuro-Oncology. 2021 5. Yang et al. Journal of Clinical Oncology. 2021 6. Bush et al. Cancer. 2023 7. Mutter et al. Lancet Oncol. 2023 8. Frank et al. ASCO. 2024 9. Efstathiou. ASTRO. 2024 10. Seidensaal et al. Radiother Oncol. 2024

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Digital Poster Partially Ablative Body Radiotherapy (PABR): A widely applicable planning technique for palliation of locally advanced unresectable tumour Adam Unjin Yeo, David Jong, Mark Burn, Therese Chesson, Siena Williams, Sarat Chander Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia Purpose/Objective: Patients with locally advanced, bulky, and unresectable tumours frequently exhibit frailty and endure symptomatic burden arising from the mass effect of their tumours. Conservative approaches may often fail to provide symptomatic benefit in relatively radioresistant, slower growing tumours such as sarcomas. The purpose of this paper is to describe a widely applicable radiation therapy protocol in detail for Partially Ablative Body Radiotherapy (PABR) technique, of which clinical results are available in the previous work [1-2]. Material/Methods: Low-dose palliation prescription of 20Gy in 5 fractions is applied to gross tumour volume (GTV) with tumour size of ≥ 5.0cm in any direction (i.e. minimum 5cm at the shortest axis). Planning target volume (PTV) with the standard 1cm margin is planned for 95% of the volume to be covered by 95% of the prescribed dose. To implement spatial fractionation, the boost target volume (GTVboost) is generated by 1.0-1.5cm contraction from the intact GTV, and planned for 90% of the volume to be covered by a simultaneous integrated boost (SIB) dose of 50Gy. Another 1.0 1.5cm contraction is applied from GTVboost to generate a hotspot planning volume to achieve a concentrically increasing dose up to 65-70Gy (D2%) confined in the middle of GTV. 10MV flattening-filter-free (FFF) beam is utilised to maximise dose-rate modulation for volumetric modulated arc therapy (VMAT). Daily CBCT images are used for delivery verification and imaging study.