The 15-ton compact accelerator is lifted into the David C. Pratt Cancer Center at Mercy St. Louis. (Photo: Business Wire)
July 23, 2021 — Mevion Medical Systems announced that it has delivered the 15-ton compact accelerator to Mercy Hospital St. Louis in Missouri. The accelerator, the world’s smallest, is the core of the MEVION S250i Proton Therapy System which precisely delivers therapeutic doses of radiation to tumors while preserving healthy tissue and critical organs.
The arrival of the accelerator commences the installation of the proton system at the David C. Pratt Cancer Center at Mercy St. Louis. The nationally accredited center provides outpatient treatment, radiation oncology and infusion services for patients throughout the Mercy network. Mevion’s unique and compact design enabled the new proton center to be embedded directly into the existing radiation oncology department. This efficient approach allows the hospital to share existing resources and offer patients all its cancer-fighting tools under one roof.
“This major milestone in construction puts us one step closer to making the Mercy Proton Therapy Center a reality for our patients,” said Steve Mackin, Mercy executive vice president and Mercy’s East Communities president. “Seeing the equipment before it’s enclosed in the concrete vault shows just how massive an undertaking this project has been. It’s remarkable to think of the many people who will survive – and thrive – because of this technology.”
The MEVION S250i features the industry-leading HYPERSCAN pencil beam scanning technology and Adaptive Aperture pMLC, a powerful duo that provides faster and more precise dose delivery, Mevion’s natively integrated CBCT imaging, and surface-guided tracking from C-RAD for high precision patient positioning and intra-fraction motion management.
“We are proud to partner with Mercy to provide this leading-edge technology,” said Tina Yu, Ph.D., CEO of Mevion Medical Systems. “Mevion’s mission is to make proton therapy accessible and the quality and value of the MEVION S250i has enabled more centers, like Mercy, to provide this powerful treatment modality to their patients.”
Reducing the size and complexity of a proton therapy system has allowed more hospitals to adopt proton therapy without the enormous expenditures and space requirements of other proton systems. Today, new proton therapy centers in the United States are almost exclusively compact single-room systems, and Mevion is the preferred compact room provider of NCI-Designated Cancer Centers. To date, over 6,000 patients have been treated on Mevion proton therapy systems, more than on any other compact system.
For more information: www.mevion.com
November 13, 2025 
