A Beijing-based company that operates radiotherapy and diagnostic imaging centers in China closed a deal that makes it the second-largest owner of the University of Texas MD Anderson Cancer Center's Proton Therapy Center.

Concord Medical Services Holdings said it acquired a 19.98% stake in the proton therapy facility through its minority investment in the facility's general partner and facility management organization. Adam Sun, Concord Medical Services' CFO, said he could not disclose the amount of the all-cash investment.

Concord Medical purchased its ownership from an undisclosed existing owner. The MD Anderson Cancer Center, a 607-bed cancer hospital in Houston, remains the largest owner of the facility.

Concord Medical is the first new investor since the facility opened in 2006, said Amy Hay, vice president of business development for the MD Anderson Cancer Center and the former CEO of the proton therapy center.

Since then, the facility has treated more than 4,000 patients, which is about 15% of the total number of patients who have received proton treatment in the U.S., Hay said. She declined to disclose the center's revenue.

Investors in the proton center include General Electric, a manufacturer of imaging technology; Hitachi, a manufacturer of proton therapy systems; the Houston Police Officer's Pension System; the Houston Firefighters' Relief & Retirement Fund; the Styles Co., a developer of healthcare facilities; and Sanders Morris Harris, an investment bank.

There are currently 10 proton-beam therapy facilities in operation in the U.S.

Concord Medical will receive management fees and cash distribution, according to the agreement. The company will also join the board of directors and the advisory committee.

Sun said Concord Medical plans to partner with local specialty hospitals in Beijing and Guangzhou to open proton centers in 2016 and will use the experience and knowledge from its investment in the MD Anderson Proton Therapy Center to operate the new centers.

"The acquisition of interest in MD Anderson Proton Therapy Center plays a key role in accelerating Concord Medical's strategic plan to build and operate proton centers in China," says Dr. Jianyu Yang, Concord Medical's chairman and CEO, in a news release.