Varian Medical Systems Inc., a maker of radiation therapy equipment, said Monday it would buy Calypso Medical Technologies Inc., which develops tumor-tracking software, for approximately $10 million.

The deal for privately held, Seattle-based Calypso also includes potential earnouts determined by product sales exceeding a certain threshold over the next 30 months.

The deal should close in October.

"With Calypso's technology, Varian will be able to offer cancer treatment centers real-time, non-ionizing tumor tracking tools for enhancing the precision of their treatments," Timothy E. Guertin, president and CEO of Palo Alto, Calif.-based Varian, said in a statement.

Calypso makes GPS for the Body and Beacon electromagnetic transponders for real-time tracking of prostate cancer tumors. It also received permission from the Food and Drug Administration to conduct a clinical trial on a yet-to-be-released device for tracking lung cancer during radiation treatments.

Calypso said it generates about $15 million in annual revenue on sales and service on 110 installed systems in North America and Europe.

Varian said the purchase, which it expects to be slightly dilutive to fiscal 2012 earnings per share, nets the company 90 current or pending patents.