3558 - Proton Beam Therapy in the Treatment of Salivary Gland Malignancies of the Head and Neck: A Single Institution Review
Presenter(s)
L. A. McGee1, M. M. Voss2, A. Rohit3, S. H. Patel1, S. C. Lester4, M. A. Neben-Wittich4, R. L. Foote4, J. C. M. Rwigema1, Y. Garces4, D. M. Routman4, J. M. Wilson5, D. L. Price6, J. R. Janus7, M. L. Hinni8, A. V. Chintakuntlawar9, K. Price9, P. Mcgarragh10, A. L. Holtzman5, and D. J. Ma4; 1Department of Radiation Oncology, Mayo Clinic, Phoenix, AZ, 2Department of Quantitative Health Sciences, Mayo Clinic, Phoenix, AZ, 3Drexel University College of Medicine, Philadelphia, PA, 4Department of Radiation Oncology, Mayo Clinic, Rochester, MN, 5Mayo Clinic, Rochester, MN, 6Department of Otolaryngology-Head and Neck Surgery, Mayo Clinic, Rochester, MN, 7Mayo Clinic, Department of Otolarynoglogy, Jacksonville, FL, 8Mayo Clinic, Phoenix, AZ, 9Division of Medical Oncology, Mayo Clinic, Rochester, MN, 10Mayo Clinic Rochester, Rochester, MN
Purpose/Objective(s): Salivary gland malignancies (SGM) are rare head and neck cancers. Historical data suggest relative radioresistance; therefore, high LET radiotherapy, such as proton beam radiotherapy (PBT), may improve tumor control while limiting toxicity. We report efficacy and toxicity outcomes for patients with SGM treated with PBT at a single institution.
Materials/Methods: Between 2016 and 2025, 132 patients with SGM of the head and neck were treated with curative-intent PBT. Patients with distant metastatic disease or prior radiotherapy were excluded. Clinical records were retrospectively reviewed to assess disease control and survival outcomes. Toxicities were prospectively recorded according to CTCAE v5.0. Histologies included salivary duct carcinoma (n=33), mucoepidermoid carcinoma (n=27), adenocarcinoma (n=20), acinic cell carcinoma (n=19), carcinoma ex pleomorphic adenoma (n=12), mammary analogue secretory carcinoma (n=4), and carcinoma not otherwise specified (n=17). Patients with adenoid cystic carcinoma were not included in this analysis. Kaplan–Meier methods were used to estimate local control (LC) and overall survival (OS). Hazard ratio and cox regression modeling was performed to evaluate associations between tumor and treatment variables and outcomes.
Results: Median follow-up was 3.04 years (range, 0–9.14). Upfront surgery was performed in 123 patients, with margin status as follows: R0 (n=75), R1 (n=43), and R2 (n=5). Nine patients were unresectable and received definitive PBT. Median PBT dose was 60.0 GyE. 78 patients had localized disease, while 54 had nodal involvement (N1 n=10, N2 n=27, N3 n=17). Locally advanced disease (T3–T4) was present in 52.3% of patients. Fifteen patients had recurrent disease without prior adjuvant radiotherapy. Primary tumors arose from minor salivary glands in 28 patients and major salivary glands in 104. The 3-year LC rate was 90.0%. Factors associated with worsened LC included perineural invasion (PNI; p=0.008), unresectable tumors (p<0.001), positive surgical margins (p=0.006), and advanced T stage (T3–T4; p=0.034). The 3-year OS rate was 88.0%, with unresectable disease predicting inferior OS (p=0.034). Acute grade 3 toxicities occurred in seven patients, most commonly mucositis, oral pain, and dermatitis; two patients required feeding tube placement. Late grade 3 toxicity was observed in six patients and included osteoradionecrosis (n=3), eustachian tube dysfunction (n=2), and cellulitis (n=1). No grade =4 toxicities were reported.
Conclusion: PBT provides excellent LC for patients with SGM with acceptable toxicity. Longer follow-up is warranted to confirm durability of outcomes.