June 14, 2005
Why Up To Eight Percent of Cancers Go Undetected
ST. LOUIS -- A few years ago, Medhat Osman, M.D., Ph.D., had a patient who was scanned due to a suspicion of lung cancer using positron emission tomography (PET) and computer tomography (CT) technology. The scan came back negative, but the patient then complained of a problem with his leg.
Osman, director of PET Imaging at Saint Louis University Hospital and assistant professor of nuclear medicine at Saint Louis University School of Medicine, opted to try a "true whole body scan" on the patient to evaluate his condition."We decided to scan his legs and detected a completely different type of malignancy that would have been missed had we had not done a true whole body scan," Osman says.
Osman and colleagues at Saint Louis University are pushing for national changes in the way PET imaging scans are performed after determining that as much as 8 percent of cancerous legions occur outside of the current imaging field. His results will be presented during the June 18-22 Society of Nuclear Medicine conference in Toronto.
Osman says medical institutions need to recognize the limitations of scanning equipment and change imaging protocols so that a patient can be screened for medical conditions from head to toe, such as cancer.
Kathleen Kiske, 50, is one of the patients in the initial clinical studies. Diagnosed with melanoma in her torso, the south St. Louis County resident underwent chemotherapy, radiation therapy and endured multiple surgeries. As she fought back from her disease, she underwent a true whole-body scan at Saint Louis University Hospital. No malignancies were found in her torso, but the scan showed a single, clear malignancy in her knee.
"That scan and the ones I have had done every four months since then have kept me alive," says Kiske. "They have found malignancies when we weren't even looking for them and in places where we didn't realize there was a problem."
Kiske has battled cancer recurrences four times. By catching her malignancies early and treating them aggressively, Kiske now has been tumor-free for almost two years.
Osman's success with the new PET imaging protocol has been presented at multiple medical conferences, including the Radiologic Society of North America, the Society of Nuclear Medicine, the Academy of Nuclear Imaging and the European Society of Nuclear Medicine.
"With the clinical results we have had at Saint Louis University Hospital, the future is clear," says Osman. "True whole-body scans with the advanced PET/CT system enable us to better diagnose and treat cancer. I think that the new true whole body PET/CT protocol that we've been testing will become the standard for all PET centers because of its noninvasive nature, large field of view, accuracy, ease of use, speed and patient comfort."
PET highlights chemical and physiological changes related to metabolism that often occur before structural damage is evident. PET is the leading diagnostic tool for oncology patients because of its high sensitivity to detect malignancies. It also can identify recurrent disease before it spreads through the body. CT imaging is used to identify anatomic, or structural, abnormalities. The technology allows radiologists to take thin detailed pictures, or "slices," of any abnormality.
Saint Louis University Hospital currently has the region's only PET scanner with 16-slice CT capability, enabling it to more rapidly obtain images and with better accuracy.
By combining CT and PET technologies, a PET/CT scanner allows physicians to accurately merge two distinct radiologic images into one image of a patient's whole body. The term "whole body," however, is misleading, because the actual image acquisition from the PET scanner typically does not include images of the brain, skull and significant portions of the arms and legs.
Osman says he and others rapidly developed ways to image the entire body within the limited field of view of the typical PET scanner two years ago.
"We started with patients diagnosed with lung cancer or melanoma, two very aggressive cancers, and found that by doing two scans encompassing the entire body from head to toe, we could rapidly identify locations where the cancer had spread beyond the traditionally scanned areas," he says. "In fact, our studies show that up to eight percent of cancerous lesions occurred outside of the main torso area and were missed by standard imaging protocols. Thanks to the unique scanning capability of acquiring the whole body from head to toe, we have made the true whole-body PET imaging protocol the standard of care at Saint Louis University Hospital with all of our patients undergoing PET/CT scans."
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