This multicenter study reported acute toxicity outcomes of patients with major salivary gland cancers registered on the Proton Collaborative Group REG001-09 trial (NCT01255748). 105 patients including parotid (N = 90) and submandibular gland (N = 15) tumors, were treated with PBT to the median dose of 66.5 GyE in 33 fractions across seven institutions.

The result shown that with the median follow-up 14.3 months, acute grade 2 or higher toxicity included nausea (1.5%), dysgeusia (4.8%), xerostomia (7.6%), mucositis (10.5%) and dysphagia (10.5%). The study concluded that PBT should be strongly considered when ipsilateral radiation therapy is indicated for major salivary gland cancer based on a considerably lower incidence of acute grade 2 or higher toxicity in this analysis compared to historical IMRT outcomes.