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| |  RSNA MEETING: Studies Argue For Wider Use Of PET In Cancer Patients CHICAGO, IL -- December 3, 1997 -- 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: 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: "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 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. "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. "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 seven to 10 days after tamoxifen therapy began. Two radioactive tracers were used: -- 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. "Normally, a patient and her physician have to wait at least two to three 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 three 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. 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 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. "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.” 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," Dr. Shreve saied. A PET scan can cost about the same as some CT or magnetic resonance (MR) imaging scans, he said. 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 nine of the patients. Active infections at 11 sites in eight patients were confirmed by laboratory tests or other imaging, Dr. "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.
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