MRI-Guided Reduced-Volume Radiation Therapy for Early-Stage Glottic Cancer:A Prospective Phase 1 Trial With Quantification of Laryngeal Motion.

PURPOSE: Five to 7 weeks of whole-larynx radiation therapy (RT) is standard for treatment of early-stage glottic cancer. Previous studies evaluated computed tomography-guided hypofractionated or stereotactic treatment to a smaller volume. Magnetic resonance-guided RT (MRgRT) allows real-time motion tracking and gating by continuously imaging the larynx. We performed the first prospective study of MRgRT in patients with early-stage glottic cancer with quantification of laryngeal motion.

METHODS AND MATERIALS: This phase 1 trial evaluated MRgRT in patients with stage I/II squamous cell glottic cancer undergoing definitive RT. The RT prescription was either 42.5 Gy/5 fractions (treatment volume <10 cm3, not actively smoking) or 58.08 Gy/16 fractions (treatment volume >10 cm3/smokers). Treatment was delivered using gated 0.35-T MRgRT with continuous tracking. Coprimary endpoints were feasibility and safety (grade 3+ toxicity rate). Patient-reported outcome measures, voice quality, MRgRT treatment parameters, and local control were assessed. Intrafraction cine-MRI quantified laryngeal motion.

RESULTS

MRgRT was feasible in all patients. Median time on study was 10.9 months. Treatment was well tolerated with no acute or late grade 3+ toxicities. There was no change in patient-reported outcome measures over the course of the study. Two patients who received 42.5 Gy experienced locoregional failure: 1 in-field only and 1 in-field and nodal. MR tracking resulted in 20/94 (21%) of treatment fractions requiring ≥1 shift necessitating intrafraction reimaging. In 19/94 (20%) of treatment fractions, the beam was off for >20% of the treatment time due to stochastic beam-interruption events. During beam-interruption events, larynx displacement exceeded 3 mm in 53% of cine-MRI frames.

CONCLUSIONS

MRgRT targeting gross disease instead of the whole larynx is feasible and safe for patients with early-stage glottic cancer with minimal treatment-associated toxicity and no detriment in patient-reported outcome measures. MRI guidance provides real-time verification of larynx position. Data regarding real-time intrafraction motion has important implications for patients receiving standard laryngeal RT.