Radiation therapy and radiosurgical service provider American Shared Hospital Services (ASHS) reported that it has increased its equity interest in proton beam radiation therapy (PBRT) device developer Still River Systems of Littleton, Mass.

 The San Francisco-based ASHS said that it has purchased $617,000 of the privately held Still River’s convertible preferred stock. This is in addition to an ASHS purchase in April last year of $2 million in the firm’s convertible preferred stock as well as an option to acquire two of Still River’s Clinatron 250 PBRT systems.

ASHS said it has contracted to place both of these devices, and expects to commence lease agreements with Tufts-NEMC and M.D. Anderson Cancer Center Orlando for the Still River PBRT systems in 2009, subject to the receipt of U.S. FDA clearance. The firm said it is currently negotiating contracts for additional PBRT systems.

The Clinatron 250 device under development by Still River Systems is a single-treatment-room PBRT system incorporating proprietary technology which may reduce the cost of implementing this Medicare-approved therapy, according to ASHS.