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For Release After 11 a.m. CST, Wednesday, Dec. 3, 1997

STUDIES ARGUE FOR WIDER USE OF PET FOR CANCER PATIENTS; TECHNIQUE ALSO MAY IMPROVE DIAGNOSIS OF INFECTIONS

CHICAGO -- New research presented today at an international scientific meeting of radiologists argues for more widespread use of a technology that is widely accepted in Europe but has had limited use in the United States. The three important studies come on the heels of an announcement by the U.S. Department of Health and Human Services that it is accelerating its review of uses for the technology, which is known as PET, or positron emission tomography.

The research presented today during the 83rd Scientific Assembly and Annual Meeting of the Radiological Society of North America (RSNA) shows that PET:

ï can determine weeks or months before conventional tests whether a cancer therapy is working;

ï is more accurate than other methods used for diagnosing and guiding treatment decisions for cancer; and

ï can pinpoint sites of infection in the body far more quickly than conventional means.

The researchers also presented information about new technology that makes PET more widely available and less expensive than in the past. PET, which is a noninvasive, nuclear medicine imaging technique that depicts metabolic changes and activity in tissues, is considered "experimental" by many insurers, which has held back its use in the United States.

The studies presented at RSNA included:

ï A Washington University School of Medicine, Mallinckrodt Institute of Radiology study of women with advanced breast cancer who were imaged with PET before treatment to determine the likelihood that their cancer would respond to the hormone tamoxifen. As early as two weeks after treatment began, PET was able to show whether the therapy was working.

ï A University of Michigan study comparing PET's ability to detect cancers with that of newer, "dual-head coincidence" cameras, which were developed as an alternative to PET. The dual-head coincidence technology missed from 10 percent to 77 percent of the cancers that were detected with PET.

ï A second University of Michigan study showing that PET appears able to pinpoint the site of suspected infections in the body within an hour -- a determination that takes from 24 hours to several days with conventional techniques. "PET has been rapidly embraced in much of Europe and, in some countries, a PET scan is required to determine whether a cancer has spread before a patient undergoes surgery. Adoption of the technology has been slower in the United States, despite the fact that it offers major advantages over other methods of cancer imaging," said Richard L. Wahl, M.D., professor of radiology and internal medicine, and director of general nuclear imaging, University of Michigan, Ann Arbor.

"PET is perceived as high-tech and, therefore, expensive by insurers and other medical decision makers," he said. "In fact, it can be very cost-effective. Making the right treatment decision can spare patients debilitating and expensive treatments that over time prove to be ineffective."

Studies have shown that approximately 30 percent of patients with tumors will have findings on PET of cancer spread that wasn't known from other imaging studies. Other studies show that PET changes treatment decisions in from 25 percent to 40 percent of cases.

With PET, patients are injected with a glucose that has been labeled with a radioactive tracer. Cells that are undergoing more metabolic activity, such as sites of infection and cancer, will take up more glucose. Positron radioactivity emitted by the radiolabeled glucose is recorded by a PET camera, processed and reconstructed by computer so that the areas of greatest metabolic activity "light up" on a computer-generated image, which is much like a conventional CT scan. Unlike the CT scan, which shows the anatomy of the patient, PET is a CT-like image of the biochemistry of living tissue. The small amount of radioactive material used in the PET scan decays quickly and poses no danger to patients.

PET and Breast Cancer Treatment

"The use of hormonal therapy for treating advanced breast cancer is determined by the 'estrogen- receptor status' of the tumor. Approximately two-thirds of breast cancers are positive for estrogen receptors, and about 55 percent to 60 percent of these patients will respond to a hormonal therapy, such as tamoxifen, that binds to estrogen receptors," said Farrokh Dehdashti, M.D., assistant professor of radiology, Washington University School of Medicine, Mallinckrodt Institute of Radiology, St. Louis. "Estrogen-negative cancers are best treated with other methods, such as chemotherapy." PET is the only imaging technique that can assess the estrogen- receptor status of breast cancer, she said.

In the research conducted by Dr. Dehdashti and her colleagues, 11 women with biopsy-proven estrogen-positive advanced breast cancer were studied with PET before treatment, and 7 to 10 days after tamoxifen therapy began. Two radioactive tracers were used:

ï FES (fluoro-estradiol), an agent that binds to estrogen-receptors. "Intense uptake of FES in the tumor before therapy suggests that the tumor will respond to a hormonal therapy like tamoxifen," Dr. Dehdashti said.

ï FDG (fluoro-deoxy-glucose), the most widely used PET radiopharmaceutical. "If a cancer is going to respond to hormone therapy, there is a metabolic 'flare' characterized by an increase in FDG-uptake in the tumor after therapy begins compared to FDG-uptake before therapy," Dr. Dehdashti said.

"Normally, a patient and her physician have to wait at least 2 to 3 months after treatment to detect clinical or radiographic anatomical changes that the tumor is -- or is not -- responding to treatment," Dr. Dehdashti said. "With PET imaging, we can answer that question within a couple of weeks.

"This is important information. If the therapy is not working, we want to change treatments right away to avoid unnecessary treatment-related side effects and the expense of an ineffective therapy."

In the study, the PET results were compared with clinical and radiologic evaluation, with follow- up from 3 to 19 months -- until the tumor became unresponsive to the tamoxifen therapy. Consistent with the PET findings, all patients who showed a high uptake of FES before treatment responded to the treatment, Dr. Dehdashti said. Four patients did not show a high uptake of FES before treatment and they did not respond to therapy, Dr. Dehdashti said.

PET and Dual-Head Coincidence Cameras

In a study from the University of Michigan, researchers compared dedicated PET scanners with dual-head coincidence cameras -- hybrid scanners that use scintillation cameras to perform both conventional nuclear medicine imaging (such as single photon emission computed tomography, or SPECT) and PET. Past studies have shown that PET scanners are useful in detecting recurrence or metastases in a number of cancers. The Michigan study focused on whether the hybrid scanners are as effective.

PET and dual-head coincidence imaging using FDG were performed on 35 patients with known or suspected cancers. A total of 121 sites of cancer were detected by PET, compared to 70 detected by the dual-head coincidence camera, according to Paul D. Shreve, M.D., assistant professor of radiology and internal medicine, University of Michigan, Ann Arbor.

The dual-head coincidence camera detected 86 percent of the lung cancers detected by PET; 58 percent of cancerous lymph nodes in the mediastinum (chest cavity); 50 percent of cancerous axillary lymph nodes; 77 percent of metastatic cancers in the rib or spine; 90 percent of cancers in the neck and 23 percent of cancers in the abdomen.

"This study demonstrates that current dual-head coincidence camera technology is considerably less sensitive than PET in the detection of small cancers," Dr. Shreve said. "The newer technique may be comparable to PET in detecting some lung cancers, and there are substantial technical improvements under development," he said.

"Dual-head coincidence cameras were developed to respond to the argument that PET is too expensive, but the costs have come down dramatically in recent years," Dr. Shreve said.

When clinical PET centers were first opened in the late 1980s, they required a capital investment that was prohibitive for many institutions and the technique was available only in large research centers. Because of the short half-life of FDG and other PET tracers, sites needed a cyclotron to produce the tracers, and a team of chemists and physicists to oversee their production, Dr. Shreve said. "This year, the first commercial network for the regional production and distribution of positron radiopharmaceuticals was established in the United States, eliminating the need for expensive on-site radiopharmaceutical production and thus making PET imaging available to far more patients," he said.

"Today, the cost of purchasing and installing a PET tomograph is about the same as some spiral CT scanners. The new coincidence cameras with PET capabilities currently cost somewhat less," said Dr. Shreve. A PET scan can cost about the same as some CT or magnetic resonance (MR) imaging scans, he said.

PET and Diagnosis of Infection

PET also shows promise as a method to enable prompt diagnosis of areas of infection within the body, said Dr. Wahl. "The speed with which the site of an infection can be pinpointed and appropriate treatment started can have a significant effect on outcomes," he said. Current methods for diagnosing infection can take from 24 hours to several days, whereas PET results can be available in an hour or less.

In the study, 11 patients suspected of harboring various bacterial infections were studied with FDG-PET. The technique correctly identified infection in 9 of the patients.

Active infections at 11 sites in 8 patients were confirmed by laboratory tests or other imaging, Dr. Wahl said. PET correctly ruled out infection in 2 patients.

"More extensive clinical evaluation is warranted to determine the accuracy of this method, including its application for imaging viral and fungal infections," Dr. Wahl said.

Reimbursement for PET

In the FDA reform bill passed by the U.S. Congress earlier this fall, there is a provision that gives the FDA two years to develop new pre-market approval and good manufacturing practices regulations for radiopharmaceuticals used with PET, Foothill Ranch, Calif.

"The absence of FDA approval has prevented Medicare from covering PET, but the new law paves the way for the Health Care Financing Administration (HCFA) to review the agents for coverage," said Jennifer S. Keppler, C.N.M.T., M.B.A., executive director, Institute for Clinical PET.

"Many private sector insurers have been reimbursing PET for years, but FDA approval has been slower than it should be because it was up to the clinicians who made the PET tracers in their own facilities to get approval from the FDA. They had to go through the same procedures that are required of pharmaceutical companies, which have more resources to devote to seeking drug approvals and are much more familiar with FDA regulations," she said.

Last month, U.S. Secretary of Health and Human Services Donna Shalala announced that Medicare will begin paying for PET scans in the diagnosis and staging of lung cancer and committed FDA to a fast track review of other uses of PET within the next 18 months, according to Ms. Keppler. "The agency has indicated it will review applications for colorectal, head and neck, melanoma, breast and ovarian cancers, and Hodgkin's lymphoma," Ms. Keppler said.

Co-authors of a paper presented by Dr. Shreve at the RSNA meeting are R. Steventon, C.N.M.T.; E. Deters, C.N.M.T.; M. Gross, M.D.; and R. Wahl, M.D.

Co-authors of a paper presented by Dr. Dehdashti during the RSNA meeting are F. Flanagan, M.D., and B. Siegel, M.D.

Co-authors with Dr. Wahl are Y. Sugawara, M.D.; S. Fisher, B.S.; P. Kison, B.S.; and K. Zasadny, Ph.D.

The RSNA is an association of 30,000 radiologists and physicists in medicine dedicated to education and research in the science of radiology. The Society's headquarters are located at 2021 Spring Road, Suite 600, Oak Brook, Illinois 60523-1860.

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Copies of 1997 RSNA news releases are available online at http://www.pcipr.com/rsna beginning Monday, Dec. 1.