LITTLETON, Mass.--(BUSINESS WIRE)--Mevion Medical Systems, the leading provider of advanced proton therapy systems, announced today that it has entered into an investment agreement where up to $200 million will be invested in Mevion to accelerate its worldwide expansion. The investment was led by HOPU Investments, YuanMing Capital, and participated in by other Chinese investors and existing U.S. investors Caxton Alternative Management L.P., ProQuest Investments, Venrock and CHL Medical Partners