MR-guided ultra-hypofractionated radiotherapy for early-stage glottic cancer: A phase I feasibility study

Ultra-hypofractionation for early-stage glottic cancer reduces the number of hospital visits, but requires precise delivery to minimize the risk of radiation-induced toxicity. Magnetic Resonance (MR)-guided radiotherapy is a delivery technique that enables visualization of the tumor and laryngeal cartilages at each treatment session. In addition, motion management provides confidence that radiation is delivered precisely to the tumor while minimizing dose to the laryngeal cartilages. This study evaluates the feasibility and safety of an MR-guided ultra-hypofractionated treatment for early-stage glottic cancer.

This is a prospective, single-center phase I feasibility study conducted at the University Medical Center (UMC) Utrecht. Twenty patients with cT1-2N0M0 squamous cell carcinoma of the glottic larynx and an indication for definitive radiotherapy will be enrolled. Active smokers and patients who do not meet the dose criteria will be excluded from the study. Patients receive 5 × 8.5 Gy, divided over three weeks (2 fractions per week). The GTV-PTV margin is 2 mm anterior-posterior, 2 mm left-right, and 4 mm cranio-caudal. The treatment is delivered on a 1.5 T MR-Linac (Elekta Unity), using online plan adaptation and motion management.

The primary endpoints are technical feasibility and safety. MR-guided ultra-hypofractionated radiotherapy will be considered feasible if at least 80% of the patients (16/20 patients) successfully complete all five treatment fractions on the MR-Linac. The treatment is considered safe if a maximum of 10% of the patients (2/20 patients) experience a grade 3 disease-free late toxicity.