Initiating Proton Ocular Treatments on General-Purpose Beamlines: Challenges and Trends From the Survey of US Facilities.

Abstract

Historically, ocular melanomas and other eye cancers accounted for a substantial share of proton therapy patients. Although the number of proton facilities in the United States increased rapidly in the last decade, as of 2025, only roughly 1 out of 6 had active ocular proton therapy (OPT) programs. Despite the robust growth in the number of proton treatments overall, eye treatments appear to have peaked in 2016. We aimed to identify barriers to the expansion of the availability of hypofractionated proton therapy for ocular cancer patients. A questionnaire was designed and distributed to proton facilities in the United States to query the level of interest in eye treatments and the challenges to establishing and supporting ocular programs. The responses were analyzed separately for the Adopters representing active programs, and the Aspirants who were not yet offering OPT. Proton therapy facilities now operate in half of the US states. However, OPT is currently delivered in only 7 states. The use of pencil beam scanning application for ocular treatments is on the rise, as older facilities employing scattering techniques work to upgrade their beamlines. Despite a substantial interest at many facilities in developing ocular treatments on general-purpose beamlines, the lack of commercialized solutions and information on best practices has been identified as a barrier. Specific areas were identified with the most acute lack of currently available guidance. Access to OPT is lagging that of proton therapy in general. Limited local accessibility, relative to alternative treatments, likely contributed to the stagnation in proton patient numbers. As the experience on non-dedicated beamlines at Adopter facilities grows, it is timely and important for the community, comprising both practitioners and vendors, to guide and facilitate establishment of new ocular programs, while maintaining the high standard of care for which OPT is known.