PET scans miss up to eight percent of cancers
13 July 2005
St. Louis, USA. According to research by Dr Medhat Osman of St Louis
University, up to 8% of cancerous lesions occur outside the current imaging
field. Whole-body scanning using combined PET/CT is needed to ensure proper
diagnosis and treatment of cancer.
A few years ago, Dr Medhat Osman, 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.
Dr 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,” Dr Osman says.
Dr 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 lesions occur outside of
the current imaging field. The results were presented during the Society of
Nuclear Medicine conference in Toronto in June 2005.
Dr Osman says medical institutions need to recognise 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 realise there was a
problem.”
Kiske has battled cancer recurrences four times. By catching her
malignancies early and treating them aggressively, Kiske now has been
tumour-free for almost two years.
Dr 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 Dr 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.
Dr 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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