Cesium-131 From IsoRay Medical (TM), Inc. Established as a Front Line Treatment for Early Stage Prostate Cancer Treatment in a Recent Clinical Trial: Results Unveiled by Renowned Researchers at American Brachytherapy Society (ABS) Annual Meeting

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Investigators of a recent multi-institutional trial, led by principal investigator Bradley Prestidge, conclude that Cesium-131, a medical isotope used in low dose (LDR) brachytherapy treatment for prostate cancer, "... has come into widespread use; and the clinical results of this trial are mature enough to be of immediate, important, practical use to practitioners."

This is one of several highly anticipated studies presented at ABS and marks a major milestone in the brachytherapy field, providing high level of confidence in the effectiveness of Cesium-131 for physicians and patients

    The study, conducted by Dr. Prestidge and Dr. William Bice, principal investigator in charge of physics & quality assurance for the Cs study, both of the Texas Cancer Clinic, measured the typical urinary and rectal responses of Cesium-131 for prostate cancer therapy. They found a correlation between dosimetry (the accurate measurement of radiation doses) and urinary and rectal responses (morbidity). The study concluded these responses are most often resolved back to baseline within four to six months.

Prestidge and Bice presented their findings from this clinical trial focusing on the safety of permanent Cesium-131 seed implantation for prostate cancer therapy at the 28th American Brachytherapy Society Annual Meeting, held in Chicago April 29th through May 1, 2007. It was one of several scientific presentations at the ABS Annual Meeting that detailed new information about the safety and efficacy of Cesium-131.

Cesium-131 is a proprietary product from IsoRay Medical(TM),Inc. a wholly owned subsidiary of a public company, IsoRay, Inc. ("IsoRay") (AMEX Symbol:ISR), based in Richland, WA.

Brachytherapy (LDR) is a treatment in which seeds containing a radiation source are implanted in and around a cancerous tumor of the prostate. Cesium-131, is the first breakthrough treatment in fighting prostate cancer in more than 20 years.

"This is one of several highly anticipated studies presented at ABS and marks a major milestone in the brachytherapy field, providing high level of confidence in the effectiveness of Cesium-131 for physicians and patients," said Dr. Steven Kurtzman, medical director for IsoRay Medical and a principal with the San Francisco area-based Silicon Valley Urology Center.

The seven-institution, phase II trial, focused on the safety of Cesium-131 implantation. This presentation addressed 80 of the 100 study patients, with an average pretreatment PSA of 6.75, who took part in the study and treated their cancers exclusively with brachytherapy. Computed tomography (CT) imaging was used to evaluate dosage and affect of the isotope on targeted areas. Evaluations were performed two weeks following the patients' implant procedure.

Dr. Prestidge is founder, CEO and medical director of the Texas Cancer Clinic and Texas Prostate Institute, both in San Antonio. He is a world-renowned lecturer, researcher and teacher in the field of cancer treatment, and has the largest seed implantation program in Texas and the South Central United States.

Dr. Bice, a medical physicist, has over 15 years' experience in the design, implementation, and evaluation of ultrasound-guided prostate implants. Under his supervision and guidance, his staff has been responsible for planning and supporting approximately 1,300 prostate implants. A sought after speaker, he has also published over 20 manuscripts on the procedure.

Cesium-131 offers patients unique advantages over other medical isotopes

Increasingly, prostate cancer patients and their doctors who decide on seed brachytherapy choose Cesium-131 treatment because of its significant advantages over Palladium-103 and Iodine-125, two other isotopes currently in use. These advantages include:

Higher Energy

Cesium-131 has a higher average energy than any other commonly used prostate brachytherapy isotope on the market. Energy is a key factor in how uniformly the radiation dose can be delivered throughout the prostate. This is known as homogeneity. Early studies demonstrate Cesium-131 implants are able to deliver the required dose while maintaining good homogeneity across the gland itself and potentially reducing unnecessary dose to critical structures such as the urethra and rectum. (1)

Shorter Half-Life

Cesium-131 has the shortest half-life of any prostate brachytherapy isotope at 9.7 days. Cesium-131 delivers 90% of the prescribed dose to the prostate in just 33 days compared to 58 days for Palladium and 204 days for Iodine-125. The short half-life of Cs-131 reduces the duration of time during which the prostate receives the irritating effects of the radiation. Early studies demonstrate Cesium-131 is well tolerated with minimal to moderate urinary symptoms that resolve relatively rapidly, within approximately 4-8 weeks. (1)

Higher Biologically Effective Dose

Another benefit to the short half-life of Cesium-131 is what is known as the "biological effective dose" or BED. BED is a way for health care providers to predict how an isotope will perform against slow versus fast growing tumors. Studies have shown Cesium-131 is able to deliver a higher BED across a wide range of tumor types than either Iodine-125 or Palladium- 103. Although prostate cancer is typically viewed as a slow growing cancer it can present with aggressive features. Cesium-131's higher BED may be particularly beneficial in such situations. (2)

For more information on the Cesium-131 cancer treatment breakthrough, visit http://www.cesium131.com.

FOOTNOTES:

(1) Prestidge B.R., Bice W.S., Jurkovic I., et al. Cesium-131 Permanent Prostate Brachytherapy: An Initial Report. Int. J. Radiation Oncology Biol. Phys. 2005: 63 (1) 5336-5337.

(2) Armpilia CI, Dale RG, Coles IP et al. The Determination of Radiobiologically Optimized Half-lives for Radionuclides Used in Permanent Brachytherapy Implants. Int. J. Radiation Oncology Biol. Phys. 2003; 55 (2): 378-385.

About IsoRay

IsoRay, Inc., through its subsidiary, IsoRay Medical, (TM) Inc., is the sole producer of the Cesium-131 brachytherapy seed, used to treat prostate and other cancers. The Cesium-131 seed offers a significantly shorter half-life than the two other isotopes commonly used for brachytherapy, which results in a substantially faster delivery of therapeutic radiation, lower probability of cancer cell survival and reduction of the longevity of common brachytherapy side effects. IsoRay is based in Richland, Washington. More information is available about IsoRay at http://www.isoray.com.

Safe Harbor Statement

Statements in this news release about IsoRay's future expectations, including: the advantages of our Cesium-131 seed, future production capabilities, development of protocols for the use of our Cesium-131 seed to treat cancers other than prostate cancer, the level of market share our seed may attain, and all other statements in this release, other than historical facts, are forward-looking statements. It is important to note that actual results and ultimate corporate actions could differ materially from those in such forward-looking statements based on such factors as physician acceptance, training and use of our products, our ability to successfully manufacture, market and sell our products, our ability to manufacture our products in sufficient quantities to meet demand within required delivery time periods while meeting our quality control standards, and our ability to enforce our intellectual property rights, and other risks detailed from time to time in IsoRay's reports filed with the SEC.

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