Anaheim-based Alliance Imaging Inc. said Monday that it bought six radiation surgery centers in California and four other states from Accuray Inc., a Sunnyvale device maker.

Terms of the deal weren't disclosed.

The centers use the CyberKnife robotic radiosurgery medical device. The device treats tumors in a non-invasive way with precise accuracy.

Alliance primarily runs diagnostic imaging centers for hospitals and doctors. It has yearly sales of about $450 million.

The surgery center acquisitions are part of a diversification into cancer treatment.

Alliance recently spent $36 million to buy eight cancer treatment centers from Bethesda Resources Inc., a unit of Sonix Medical Resources Inc. of New York.

The expansion comes as Alliance has seen hospitals open their own diagnostic imaging centers and as insurers look to check the use of medical scanning.