LITTLETON, Mass. — Mevion Medical Systems has introduced the MEVION S250-FIT Proton Therapy System, a proton therapy system designed for installation in a standard radiation therapy LINAC vault.
The Littleton-based company is presenting the system to the European radiation oncology community at ESTRO 2026. Mevion said the technology creates a new pathway for cancer centers to add proton therapy to existing radiotherapy programs without building a separate proton therapy facility.
The S250-FIT has been cleared by the U.S. Food and Drug Administration and is CE-marked under European Union medical device regulations. The system is designed to fit within existing LINAC-based treatment environments, aligning proton therapy with the infrastructure, workflows and capital planning already used by many radiation oncology programs.
On April 7, Stanford Medicine unveiled the world’s first S250-FIT installation, developed in collaboration with Leo Cancer Care. The system was installed inside a standard 110-square-meter, or 1,200-square-foot, LINAC vault at the existing Stanford Medicine Cancer Center in Palo Alto, Calif., without construction of a new building.
“With FIT™, proton therapy is no longer limited by infrastructure,” said Tina Yu, Ph.D., CEO and President of Mevion Medical Systems. “For the first time, it can be deployed within the same clinical and operational framework as conventional radiotherapy. For European health systems that have long recognized the benefits of proton therapy but faced significant infrastructure and financial barriers, this changes the question from whether to build a separate proton facility to how to integrate proton therapy into the radiotherapy programs they already operate.”
The S250-FIT delivers intensity-modulated proton therapy using Mevion’s HYPERSCAN pencil beam scanning technology with the Adaptive Aperture proton multi-leaf collimator. The system is also designed to support DirectARC proton arc therapy, advanced image-guided and adaptive workflows, and FLASH research.
The system is paired with Leo Cancer Care’s Marie Upright Patient Positioning and CT Imaging System, a commercial upright treatment platform with integrated diagnostic CT. Mevion said the platform may offer benefits in patient comfort and help support organ motion management during treatment.
The S250-FIT shares its core technology with the MEVION S250i, which is in clinical operation at Siteman Cancer Center at Washington University School of Medicine in the U.S. and at ZON-PTC at Maastro Clinic in the Netherlands. Mevion said that gives the company more than a decade of combined U.S. and European clinical experience with compact, single-room proton therapy.
The company said it has signed contracts with nine institutions globally for the S250-FIT, including Stanford Health Care, Loma Linda University Health, UNC Health, BayCare Health System, Atlantic Health System and the University of Nebraska Medical Center.
