IsoRay Inc. is buying back up to a million shares of the company's common stock.

The board of directors authorized the plan, the Richland-based medical isotope company announced Tuesday. Dwight Babcock, IsoRay's interim CEO, said the repurchase will "increase share holder value at a time when we believe the shares are currently undervalued in the market."

Repurchase may be conducted in the open market or in privately negotiated transactions.

IsoRay manufactures Cesium-131 brachytherapy seeds, mostly used to treat prostate cancer.