Proton Therapy for Major Salivary Gland Cancer: Clinical Outcomes.

To report clinical outcomes in terms of disease control and toxicity in patients with major salivary gland cancers (SGCs) treated with proton beam therapy. Clinical and dosimetric characteristics of patients with SGCs treated from August 2011 to February 2020 on an observational, prospective, single-institution protocol were abstracted. Local control and overall survival were calculated by the Kaplan-Meier method. During radiation, weekly assessments of toxicity were obtained, and for patients with ≥ 90 days of follow-up, late toxicity was assessed. Seventy-two patients were identified. Median age was 54 years (range, 23-87 years). Sixty-three patients (88%) received postoperative therapy, and nine patients (12%) were treated definitively. Twenty-six patients (36%) received concurrent chemotherapy. Nine patients (12%) had received prior radiation. All (99%) but one patient received unilateral treatment with a median dose of 64 GyRBE (relative biological effectiveness) (interquartile range [IQR], 60-66), and 53 patients (74%) received intensity-modulated proton therapy with either single-field or multifield optimization. The median follow-up time was 30 months. Two-year local control and overall survival rates were 96% (95% confidence interval [CI] 85%-99%) and 89% (95% CI 76%-95%], respectively. Radiation dermatitis was the predominant grade-3 toxicity (seen in 21% [n = 15] of the patients), and grade ≥ 2 mucositis was rare (14%; n = 10 patients). No late-grade ≥ 3 toxicities were reported. Proton beam therapy for treatment of major SGCs manifests in low rates of acute mucosal toxicity. In addition, the current data suggest a high rate of local control and minimal late toxicity.

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Conflicts of Interest: Steven J. Frank, MD, is an Associate Editor of the International Journal of Particle Therapy. Dr Frank reports grants and personal fees from Hitachi. Outside the submitted work, Dr Frank is a cofounder of C4 Imaging, LLC, for which he reports grants and personal fees, and he reports personal fees from Varian, grants from Eli Lilly, grants from Elekta, other remuneration from Breakthrough Chronic Care, personal fees from Augmenix, and personal fees from the National Comprehensive Cancer Center (NCCN). C. David Fuller, MD, PhD, received funding and salary support from the National Institutes of Health (NIH), National Institute of Biomedical Imaging and Bioengineering (NIBIB), Research Education Programs for residents and clinical fellows grant (R25EB025787-01); the National Institute for Dental and Craniofacial Research Establishing Outcome Measures award (1R01DE025248/R56DE025248), and the Academic Industrial Partnership grant (R01DE028290); the National Cancer Institute (NCI) Early Phase Clinical Trials in Imaging and Image-Guided Interventions program (1R01CA218148); an NIH/NCI Cancer Center Support Grant (CCSG) pilot research program award from the University of Texas MD Anderson CCSG radiation oncology and cancer imaging program (P30CA016672); an NIH/NCI Head and Neck Specialized Programs of Research Excellence (SPORE) developmental research program award (P50 CA097007); an NIH Big Data to Knowledge (BD2K) program of the NCI Early Stage Development of Technologies in Biomedical Computing, Informatics, and Big Data Science award (1R01CA214825); the National Science Foundation (NSF), Division of Mathematical Sciences, Joint NIH/NSF Initiative on Quantitative Approaches to Biomedical Big Data (QuBBD) grant (NSF 1557679); the NSF Division of Civil, Mechanical, and Manufacturing Innovation (CMMI) grant (NSF 1933369); the Stiefel Oropharyngeal Research Fund of The University of Texas MD Anderson Cancer; and the MD Anderson program in image-guided cancer therapy. Dr Fuller has received direct industry grant support, in-kind hardware, honoraria, and travel funding from Elekta AB. The other authors have no conflicts of interest to disclose.