Mevion Announces First Clinical Treatment on the MEVION S250-FIT™ Proton Therapy System

Stanford Medicine Cancer Center delivers the world’s first patient treatment using an ultra-compact proton therapy system installed in an existing conventional radiation therapy vault

LITTLETON, Mass.--(BUSINESS WIRE)--Mevion Medical Systems, a global leader in compact proton therapy, today announced that the world’s first clinical proton therapy treatment delivered inside an existing conventional radiation therapy vault has been completed at Stanford Medicine Cancer Center. The treatment was delivered on the MEVION S250-FIT Proton Therapy System™.

The milestone establishes a new category of proton therapy delivery: a compact single-room system that fits within existing radiation oncology infrastructure, eliminating the need for dedicated proton therapy bunker construction while enabling high-quality CT image guidance directly at the treatment position. For Stanford Medicine, the approach resolved long-standing space constraints in Palo Alto and accelerated the integration of advanced particle therapy into its existing oncology program.

A New Architecture for Proton Therapy

The MEVION S250-FIT™ pairs Mevion’s compact fixed-beam proton delivery with Leo Cancer Care’s MARIE^® platform, which provides 360-degree patient rotation and integrated upright CT imaging. The result is a proton therapy configuration that removes the rotating gantry, reduces the structural footprint to that of a conventional radiation therapy vault, and supports image-guided proton therapy within existing radiation oncology infrastructure.

The Stanford project was supported by Stantec (architectural design), NELCO (radiation shielding door systems), and RaySearch* (treatment planning software).

A Defining Moment for the Field

“Today’s milestone marks a turning point, not only for Mevion, but for the broader radiation oncology community,” said Tina Yu, Ph.D., CEO and President of Mevion Medical Systems. “We have validated a new class of ultra-compact proton therapy: a modular alternative to conventional X-ray linacs that fundamentally changes the equation around space, cost, and access. By removing the infrastructure barriers that have historically defined this field, we are helping more health systems bring proton therapy to their patients.”

Dr. Yu continued: “This platform is also built for what comes next. The MEVION S250-FIT™ is designed to support DirectARC™, daily online adaptive proton therapy, FLASH novel treatment techniques, and continued advances in robustness and LET optimization, the capabilities that will define the next decade of clinical proton therapy.”

Building Momentum Toward Broader Adoption

The Stanford treatment is the first clinical validation of the MEVION S250-FIT system, an FDA-cleared and CE-marked product. Additional installations are expected to follow in 2026 and beyond across North America, Europe, and Asia, including projects with BayCare, Atlantic Health System, University of Nebraska Medical Center, Loma Linda University Medical Center, UNC Health, Dana-Farber Cancer Institute, followed by international projects with Istituto Nazionale Tumori IRCCS Fondazione G. Pascale and Tam Anh General Hospital Partner. These institutions represent a growing movement toward right-sized, infrastructure-compatible proton therapy programs designed to accelerate deployment, optimize capital investment, and support long-term clinical scalability.

Rather than requiring standalone proton facilities, emerging compact proton platforms are enabling health systems to integrate advanced particle therapy directly into existing radiation oncology environments. This phased, infrastructure-compatible approach may significantly expand the range of institutions able to deploy proton therapy in the coming decade.

*RaySearch products are subject to regulatory clearance in some markets.

About Mevion Medical Systems

Mevion Medical Systems is a leading provider of compact proton therapy systems for cancer care. Dedicated to advancing the design and accessibility of proton therapy worldwide, Mevion pioneered the single-room platform and continues to further the science and application of proton therapy. Since 2013, Mevion compact single-room proton therapy systems have been used by leading cancer centers to treat patients. Mevion’s product portfolio, including the flagship MEVION S250i^® and MEVION S250-FIT™ systems with HYPERSCAN^® pencil beam scanning, represents the world’s most compact proton therapy solutions—eliminating the traditional obstacles of size, complexity, and cost. Mevion is headquartered in Littleton, Massachusetts, with a presence in Europe and Asia. For more information, please visit www.mevion.com.