Proton Therapy Outcomes for Head and Neck Cutaneous Melanoma: Proton Collaborative Group Analysis.

Purpose: Reports of proton beam therapy (PBT) utilization for cutaneous melanoma of the head and neck (HN) region is virtually non-existent. This study reports on the efficacy and acute toxicities of PBT for primary HN cutaneous melanoma.

Materials and methods: We queried the prospectively collected, multi-institutional Proton Collaborative Group registry for all consecutive patients with HN cutaneous melanoma receiving PBT from May 2010 to December 2019. Kaplan-Meier methods were used to estimate overall survival (OS), progression free survival (PFS), and local regional recurrence free survival (LRFS). Toxicity was reported per CTCAE version 4.0.

Results: A total of 8 patients were identified with a median age of 69 (range, 37-88). All patients (100%) underwent surgery followed with postoperative PBT. There were 3 patients (37.5%) with T3 or T4 disease and 4 (50%) with N2 or N3 disease. The median radiation dose was 46 GyRBE (range, 27-70) and median dose per fraction was 2.4 GyRBE (range, 2.0-6.0) with the most common dose fractionation being 44 or 48 GyRBE in 20 fractions (n = 4). At a median follow-up of 40.1 months (range, 1.6-62.4) the 1 and 3 year OS rates were 85.7% and 35.7%, respectively. The median PFS was 25.40 months (95% CI, 2.53-58.70) while PFS at 1 year and 3 years was 85.7% and 35.7%, respectively. LRFS was 100% at 1 year and 85.7% at 3 years. Five of the 8 patients developed distant metastases, of which 3 received immunotherapy. Acute G2+ and G3+ toxicities occurred in 5 of 8 patients and 2 of 8 patients, respectively. G3 toxicities included radiation dermatitis (n = 1) and immunotherapy-related rash (n = 1). No G4+ toxicities were reported.

Conclusion: Single modality PBT for HN melanomas in the definitive setting provides effective and durable local control rates with tolerable acute toxicity. Distant failure remains the primary pattern of failure.