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Staff Accomplishments

Cesium-131 dreams become reality

October 2004
The clinical benefits of a high energy, short half-life isotope are now available through the development of the cesium-131 brachytherapy seed. Cesium-131 can now be used to treat prostate cancer thanks to an efficient and affordable separation and purification process developed by the staffs of Pacific Northwest National Laboratory and IsoRay Medical Inc. Through a series of cooperative research agreements, researchers at PNNL and IsoRay have worked to develop a brachytherapy seed that uses cesium-131, a low-dose isotope. In low-dose brachytherapy, tiny capsules or seeds filled with a radioactive isotope are implanted near or in the cancerous tumor. Using the new cesium-131 procedure, approximately 30 kiloelectronvolt (keV) x-rays are emitted by each capsule. The x-rays damage the genetic material of the cancer cells, making it impossible for these cells to continue to grow and divide. Cesium has not been used in brachytherapy to treat prostate cancer before because of problems separating and purifying the isotope. With cesium-based brachytherapy, "more power or dose is delivered to the tumor over a shorter time," said project manager Lawrence Greenwood. Approximately five years ago, PNNL began working with IsoRay. The company had a patented, innovative process that efficiently produced ultra pure cesium-131. PNNL and IsoRay developed and refined the manufacturing process which deposits the cesium-131 onto a ceramic core and inserts the core into titanium capsules. This process can be easily scaled up to be commercially viable on the manufacturing level. "IsoRay selected PNNL because of our experience and expertise in working with radioisotopes," said Process and Measurement Technology Product Line Manager Wally Weimer. In addition, IsoRay's Don Segna said, "It was cheaper and quicker than building our own facility when considering the operating cost of a facility over the 4 year R&D phase and the cost of equity in our early stages." The process begins with a slug of barium carbonate. This whitish material is placed inside a research reactor at the University of Missouri. In the reactor, the barium carbonate is changed into radioactive barium-131. Over time, the barium-131 parent decays into the desired cesium-131 daughter. The university ships the material in a special lead-lined container to PNNL's Radiochemical Processing Laboratory. "PNNL's unique expertise in radiochemical separations science and materials handling attracted IsoRay to RPL to support its initial seed preparation activities. The first shipment is the culmination of five years of joint research and testing," said RPL Manager Jim Buelt. At the RPL, approximately two weeks after the barium carbonate was first irradiated, PNNL separates the cesium from the other materials in the slug. This work is done in RPL's hot cells because of gamma irradiation emitted by the barium-131 parent. Because the cesium-131 daughter only emits low-energy x-rays, it can easily be handled in a fume hood or glove box. The cesium is then placed onto a ceramic core. The core is then placed inside a titanium capsule, which is about the size of an uncooked grain of rice. Next, IsoRay welds a small cap onto the canister using a laser. Because the capsule is so small, the welding originally presented some challenges. So, along with finding the optimum welding parameters, IsoRay developed a way to magnify the work on a monitor, making the welding easier and more efficient. Using a delicate laser, the welder seals the cap on each end of the capsule. Welded shut and washed to remove any contamination, the capsule is sent to the hospital where it will be loaded into needles for implantation in the patient. At this point, PNNL's and IsoRay's work is in the skilled hands of oncologists and other physicians who inject the seeds in a pattern in or around the cancerous tumor. In addition to helping develop the process, PNNL conducted an extensive series of tests to gain the data needed for FDA approval. PNNL also conducted tests on the separation methods for IsoRay, helping them gather the data they needed to make commercial and technical decisions. IsoRay, a private company based in Richland, Wash., is planning their own manufacturing plant in the Tri-Cities, Wash., for the seed production. Contacts: Larry Greenwood, 509-376-6918,, or Walter Weimer, 509-375-6922,

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