ESTRO 2025 - Abstract Book

S1527

Clinical – Mixed sites & palliation

ESTRO 2025

Results: The use of a gantry-less PT system resulted in superior dosimetry compared to photon IMRT, with significant dose reductions to OARs, including the brainstem and spinal cord. At 3-month follow-up (n=14), 85.7% of cases were curable with high local control rates (Figure 1). Most acute toxicities were grade 1 or 2, with fatigue (45%), mucositis (31.3%) and dermatitis (55%). Grade 3 toxicities were limited to one case of ocular perforation, oral pain, dysphagia and trismus. There were no treatment-related deaths.

Figure 1: Local Control at 3 months (n=14). Conclusion:

This study is the first clinical evaluation of a novel gantry-less image-guided PT system for recurrent HN and brain cancer. The PT reduced radiation exposure to healthy tissue, which is critical for re-irradiation. Furthermore, the implementation of image guidance ensured the accuracy of the treatment delivery. An interim analysis of 20 patients demonstrated promising results, with 64.3% achieving a complete response and no disease progression at three months. The proton gantry-less system exhibited dosimetric advantages over photon-based IMRT, reducing doses to organs at risk and providing superior target coverage. This cost-effective setup could expand global access to PT while maintaining a high standard of care for patients with recurrent HN and brain cancer. References: 1. Feldman J, Pryanichnikov A, Achkienasi A, Polyansky I, Hillman Y, Raskin S, Blumenfeld P, Popovtzer A, Marash M. Commissioning of a novel gantry-less proton therapy system. Front. Oncol. 2024 Nov 7;14:1417393. doi: 10.3389/fonc.2024.1417393. 2. Feldman J, Pryanichnikov A, Shwartz D, Hillman Y, Wygoda M, Blumenfeld P, Marash M, Popovtzer A. Study of upright patient positioning reproducibility in image-guided proton therapy for head and neck cancers. Radiother Oncol. 2024 Oct 10;201:110572. doi: 10.1016/j.radonc.2024.110572. Keywords: proton therapy, gantry-less, re-irradiation

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Digital Poster Gastro-intestinal toxicity: NTCP models based on CT-guided online adaptive SBRT for abdominal lymph node oligometastases

Lucy A van Werkhoven, Maaike T.W. Milder, Mischa S. Hoogeman, Remi A. Nout, Joost J Nuyttens Radiotherapy, Erasmus MC Cancer Institute, University Medical Center, Rotterdam, Netherlands