ESTRO 2025 - Abstract Book

S945

Clinical – Head & neck

ESTRO 2025

4 Division Medical Physics, Karl Landsteiner University of Health Sciences, Krems an der Donau, Austria. 5 Division Radiation Oncology, Karl Landsteiner University of Health Sciences, Wiener Neustadt, Austria

Purpose/Objective: Late severe mucosal ulceration/ hemorrhage is rare but potentially fatal toxicity following hypofractionated carbon ion therapy (CIRT) for head and neck cancers. We investigated Mucosa-sparing-strategy (MS-CIRT) to minimize late mucosal complications.

Material/Methods:

Plans and clinical outcome of 56 patients with non-squamous head and neck cancer were evaluated. 33 patients were treated with standard optimization (without MS-CIRT) and 23 with MS-CIRT. Mucosa-to-spare (MTS) structures were created by contouring 2 mm strip of soft-palate, pharyngeal and oral mucosa in the region of high-dose PTV (HD-PTV) (Figure 1a-c). MSS-CIRT-plans were prescribed to D RBE|LEM-I|50% = 68.8 (65.6-73.6) Gy /16 fraction (4 fractions/week) using the local effect model-I (LEM-I) optimization. Additionally, doses were recalculated using the modified