Mevion Medical Systems announced that it has closed a $45 Million investment from ProQuest Investments and its existing investors, including Caxton Heath Life Sciences, Venrock and CHL Medical Partners. Mevion is the manufacturer of the MEVION S250 Proton Therapy System. The capital will be used to accelerate the manufacturing and worldwide deployment of the MEVION S250.

Proton beam radiation therapy permits more precise dose targeting by complete proton absorption at predictable tissue depth, allowing the treatment of target volumes adjacent to critical structures without inadvertent dose to sensitive structures. The availability of proton therapy has remained very limited however, due to the enormous cost, large footprint, and technical complexity of traditional proton systems. Powered by a TriNiobium Core™, the MEVION S250 significantly reduces the cost, size and complexity to levels similar to other modern X-ray radiation therapy devices, and brings accessibility, affordability and practicality to proton therapy.

"We welcome the new endorsement by ProQuest Investments and the continuing support of our existing financial partners," said Joseph K. Jachinowski, Chief Executive Officer of Mevion Medical Systems. "With delivery of our first system complete and with two additional systems now under installation, this investment will support the growing demand for our innovative technology. We are also pleased to welcome Mr. Jay Moorin of ProQuest Investments onto the Mevion Medical Systems' Board of Directors," stated Jachinowski.

The MEVION S250 Proton Therapy System has not yet been cleared by the United States Food and Drug Administration for clinical use.

About ProQuest Investments
ProQuest is a healthcare venture capital firm with offices in Princeton, San Diego and Montreal. ProQuest invests in healthcare companies seeking financings from seed to late-stage. ProQuest's portfolio reflects the rich diversity of the healthcare industry and exemplifies our commitment to fostering the growth of exceptional businesses. For more information, please visit ProQuest's website at www.proquestvc.com.

About Venrock
Venrock is a premier venture capital firm with offices in Palo Alto, New York, Cambridge, MA, and Israel. Originally established as the venture capital arm of the Rockefeller family, Venrock continues a seven-decade tradition of partnering with entrepreneurs to establish successful, enduring companies. For more information, please visit Venrock's website at www.venrock.com.

About CHL Medical Partners
CHL Medical Partners is a premier venture capital firm dedicated to partnering with entrepreneurs and inventors to create and finance innovative biotechnology, molecular diagnostic, healthcare service and medical device companies. For more information, visit www.chlmedical.com.

About Mevion Medical Systems
Mevion Medical Systems, Inc. (formerly Still River Systems, Inc.) is a radiation therapy company dedicated to advancing the treatment of cancer. As the pioneering developer of modern proton therapy systems, Mevion provides innovative, safe, and effective solutions by transforming advances in medical technology and science into practical clinical reality.

Mevion's flagship product, the MEVION S250 Proton Therapy System, is designed to preserve all of the treatment benefits of traditional proton therapy systems while removing the obstacles of size, cost, and complexity. Realizing this vision, Mevion has forever changed the economics and accessibility of proton therapy worldwide.

Founded in 2004, Mevion is a privately held company headquartered in the Boston metropolitan area with international offices in the United Kingdom and Japan.