ESTRO 2025 - Abstract Book

S955

Clinical – Head & neck

ESTRO 2025

1082

Digital Poster Stereotactic radiotherapy for cT1-2 glottic larynx cancer on MR-Linac: preliminary results of a treatment planning study Sabine M.L. Linden, Eric Brand, Mariëlle E.P. Philippens, Mischa de Ridder Radiotherapy department, Universitair Medisch Centrum Utrecht, Utrecht, Netherlands Purpose/Objective: Oncological outcomes for early-stage glottic cancer are good when using conventional or mildly hypofractionated fractionation schemes consisting of 25-35 fractions. Stereotactic ablative radiotherapy for early stage glottic cancer would reduce patient burden and hospital workload compared to conventional radiation therapy. A prior phase II study demonstrated promising results with minimal toxicity and good clinical outcomes for a stereotactic fractionation scheme (5x8.5 Gy) using non-coplanar VMAT on a conventional linac. The integration of MR-Linac for this treatment enables daily adaptive planning, which can reduce treatment margins. The objective of this planning study is to evaluate whether similar dose levels as reported in the phase II study can be achieved for a 5-fraction MR-Linac treatment. Material/Methods: Five patients diagnosed with cT1-2 glottic cancer were included in this planning study. CT-imaging was utilized for target and OAR delineation and optimization of MR-Linac treatment plans. The GTV-PTV margin was 2mm and in cranio-caudal direction, a margin of 5mm was used. Treatment plans were optimized to achieve a dose of 42.5 Gy on the PTV. Dose constraints were set on the ipsilateral arytenoid (D max0.03cc <=43 Gy, D mean <=30 Gy), contralateral arytenoid (D max0.03cc <=26.2 Gy, D mean <=15.2 Gy), cricoid (D max0.03cc <=45 Gy) and thyroid cartilage (D max0.03cc <=45.5 Gy). Results: The treatment plans covered 100% of the GTV with 42.5 Gy for all patients. PTV-coverage of 42.5 Gy exceeded 95% in each case. In figure 1, a visualization of the delineation and dose distribution can be found. For all patients, the dose on the laryngeal cartilages stayed below the set dosimetric constraint. The D max0.03cc to the arytenoid cartilages ranged from 14.1 to 39.8 Gy, with a D mean between 10.9 and 28.6 Gy. For the cricoid cartilage, the D max0.03cc ranged from 30.0 to 44.2 Gy, while for the thyroid cartilage the maximum dose varied between 44.0 and 44.9 Gy. Figure 2 shows the dose on the laryngeal cartilages.

Figure 1. Example CT, contouring and dose distribution of a patient with a cT1a laryngeal tumor. a) CT scan. b) delineation (red: GTV, pink: PTV, light blue: ipsilateral arytenoid cartilage, green: contralateral arytenoid cartilage, dark blue: thyroid cartilage, yellow: cricoid cartilage). c) dose distribution (orange: 42.5 Gy, light blue: 30 Gy, dark blue: 10 Gy)