Scientific findings on Proxcelan™ brachytherapy seeds (Cesium-131) presented at 26th Annual AAPM meeting for innovative research and development

RICHLAND, Washington -- The annual conference of the American Association of Physicists in Medicine (AAPM) in Minneapolis, Minn. July 22-26, 2007 was the venue for the unveiling of several scientific studies that presented evidence supporting the unique characteristics and advantages of Proxcelan™ brachytherapy seeds (Cesium-131 seeds) used in the treatment of prostate cancer and under research for other malignancies.

The studies add to the growing body of scientific research that supports the effectiveness and specific advantages of the medical isotope Proxcelan in treating prostate cancer.  Proxcelan is a proprietary product of IsoRay Medical™ - a wholly owned subsidiary of a public company, IsoRay, Inc. (“IsoRay”) (AMEX Symbol: ISR), based in Richland, WA.

Among the researchers delivering their findings on Proxcelan were Steven G. Sutlief, Ph.D., Veterans Affairs-Puget Sound Health Care System Seattle and Jeffrey Musmacher, MS, RT, Chief Radiation Therapist at Huntington Hospital, Huntington, NY.

The purpose behind Dr. Steven Sutlief’s abstract, entitled Cesium-131 Prostate Brachytherapy and Treatment Plan Parameters, was the evaluation of the radial dose fall-off for Cs-131 relative to the other two isotopes currently in use.  The study investigated the relationship between plans using available prostate brachytherapy isotopes (Cs-131, Pd-103, I-125) based on the size of the prostate and the activity of the seeds.

Treatment plans were generated for prostate volumes using the VariSeed Treatment Planning System (Varian Medical Corp.).  Seed activity was based on current clinical standards for appropriate seed activities by isotope. Identical seed arrangements were used for each of the three isotopes.

While the D90s (dose delivered to 90% of the gland) for each configuration were within 8% of each other, the V200 (percent of gland that receives 200% of the dose) range was much greater (within about 26% of each other relative to the prescription dose). The ratio of seeds needed for a large prostate relative to a small prostate was less for Cs-131 compared to I-125.

“This study shows how the greater range of radiation from Cs-131 leads to treatment plans with more even dose distributions and, in the case of large prostates, require relatively fewer seeds. This greater range of Cs-131 radiation leads to presumably greater robustness against seed replacement error,” said Steven Sutlief, PhD.

Jeff Musmacher of Oncology Professionals Management, presented his abstract entitled Dosimetric Comparison of Cesium-131 and Palladium-103 for Permanent Prostate Brachytherapy. 

The Musmacher study evaluated treatment planning differences between Cs-131 and Pd-103 for prostate brachytherapy. This study focuses on seed count, dose to the surrounding critical structures (rectum, bladder, and urethra) and the homogeneous dose distribution.

Thirty patients were planned using Varian software, both with Palladium-103 and Cesium-131  for  monotherapy, to   a   prescribed  dose of 125 Gy, and 115 Gy respectively. The average gland size was 28.48 cc.   Treatment plans were developed using an activity of 2.0u for both isotopes.  All contours of the prostate were identical between the isotopes for each patient. 

“In the series, there was a decrease of 18% planned seeds (70 versus 59) and 6% planned needles (18 versus 17) when planning for Cesium-131 as compared to Palladium-103.  There was  a decrease in the V150 (percent of gland that receives 150% of the dose) of 36%  (39% for Cesium-131 versus 61% for Palladium-103), while maintaining an average D90 (dose delivered to 90% of the gland) of 115% for Cesium-131 and 115%  for Palladium-103.  There was a decrease in the R100 (percent of rectum that receives 100% of dose) of 44% (0.15cc for Cesium-131 versus 0.28cc for Palladium-103).  A small decrease in U10 (percent of urethra that receives 10% of dose) of 2% was also noted,” stated Jeff Musmacher  about his study.

The initial conclusions of this ongoing study indicate “Treatment with Proxcelan seeds (Cesium-131) allows patients to receive the full prescription dose of cancer killing radiation to the prostate, while receiving less overdosing of the gland when compared with Palladium-103 brachytherapy,” said Musmacher.  “More mature data from this series will be presented at the 2007 ASTRO Annual Meeting this fall.”

“The evidence demonstrating the clinical benefits of Proxcelan for patients and physicians is growing,” said IsoRay Chairman and CEO Roger Girard. “The responses from physicians and physicists following major conferences, including AAPM, have been outstanding this year.”

Additional scientific studies on Proxcelan also presented

Other studies presented at the conference that supported the efficacy, value and preference for Proxcelan in brachytherapy treatment include:  Determination of TG-43 Parameters for Cesium-131 Model CS-1R2 Seed Using Radiochromic EBT Film Dosimetry, by S. Chiu-Tsau; and Dosimetric Characterization of Model CS-1 Cesium-131 Source by Thermoluminescence Dosimetry in Liquid Water, by R. Tailor & G. Ibbott.

Documented advantages of Proxcelan over other isotopes

Proxcelan 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
Proxcelan™ with 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 Proxcelan 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-103 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 Proxcelan 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 Proxcelan cancer treatment breakthrough, visit www.cesium131.com

Medicare / Medicaid
Medicare and Medicaid have established a specific reimbursement code for Proxcelan and insurance companies also cover low-dose (LDR) seed brachytherapy.
 
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.

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About IsoRay

IsoRay, Inc., through its subsidiary, IsoRay Medical,™ Inc., is the sole producer of the Proxcelan™ with Cesium-131 brachytherapy seed, used to treat prostate and other cancers. Proxcelan 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 www.isoray.com.

Safe Harbor Statement

Statements in this news release about IsoRay's future expectations, including: the advantages of our Proxcelan Cesium-131 seed, development of protocols for the use of our Proxcelan Cesium131 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" within the meaning of the Private Securities Litigation Reform Act of 1995 ("PSLRA"). This statement is included for the express purpose of availing IsoRay, Inc. of the protections of the safe harbor provisions of the PSLRA. 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, our ability to enforce our intellectual property rights, whether additional studies support the conclusions of early clinical studies, and other risks detailed from time to time in IsoRay's reports filed with the SEC.

Media Contacts:

Lori Woods, Vice President, IsoRay, Inc.
206.604.6400 (cell) 
lwoods@isoray.com

Ralph Schatzmair, Director--Investor Relations
IsoRay, Inc. 416.322.2225
rschatzmair@isoray.com

Jonathan Hunt, Chief Financial Officer
IsoRay, Inc. 509.375.1202
jhunt@isoray.com

The Bartlett Group Public Relations Barry Bartlett
206.285.0673; Cell: 206.335.4694
barry@bartlettgrouppr.com

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