Oncologists have found a new use for IsoRay's medical radioisotope Cesium-131.

The brachytherapy seeds have been used to treat prostate cancer since 2004 and on Wednesday doctors at Boston's Tufts-New England Medical Center implanted Cesium-131 seeds in several patients to treat their eye cancer.

It's the first time IsoRay's product, which is marketed as Proxcelan, has been used to treat intraocular melanoma, said IsoRay Chairman and CEO Roger Girard over the phone from Russia where he's on a business trip. IsoRay is based in Richland.

It's a milestone for the company, he said. Cesium-131 has been cleared by Federal Drug Administration for the treatment of soft tissue cancers.

Cesium-131's higher energy and homogeneity of dose rate makes IsoRay's brachytherapy seeds a better alternative than other medical isotopes such as Iodine-125 for treating eye and other types of cancers, he said.

Cesium-131's half-short life means radiation leaves the body sooner and its quick decay rate and high energy also mean less collateral damage to healthy tissues, Girard said.

He said IsoRay is working with leading medical centers in the U.S. for a clinical study next year to treat lung cancer with Cesium-131.

This week three patients received Cesium-131 implants - encased in a small disc-shaped shield with a protective gold backing - for intraocular melanoma at Tufts-New England Medical Center. The plaques are expected to be removed Monday.

Also, IsoRay is developing a variety of "delivery tools" to help treat cancers in different parts of the body, he said.

Girard said he's excited IsoRay has been able to demonstrate the relative efficiency of its signature product, Cesium-131.