PET/CT imaging proves golden for detecting cancer in children

Dec 13 2007

PET/CT imaging exhibits significantly higher sensitivity, specificity and accuracy than conventional imaging when it comes to detecting malignant tumors in children, according to research published in the December issue of the Journal of Nuclear Medicine.

And that's not all: PET/CT imaging provides doctors with additional information about cancer in children, possibly sparing young patients from being overtreated.

“PET/CT is useful in finding small tumors in small children and is a promising imaging tool in evaluating pediatric malignancies,” said Richard L. Wahl, the Henry N. Wagner, Jr., M.D., Professor in Nuclear Medicine at Johns Hopkins Medical Institutions in Baltimore, Md. “In our study, we found that PET/CT can detect small lymph node lesions diagnosed as negative with conventional (or anatomical) imaging and deny the presence of active disease in soft-tissue masses post-treatment—especially in children with a wide range of malignant cancers,” explained the Hopkins professor of radiology and oncology. “Using PET/CT could help spare children from overtreatment while fighting their disease,” he added.

There are few findings about the use of PET/CT imaging in comparison with conventional imaging with pediatric patients, said Wahl, explaining that investigators retrospectively reviewed cases to evaluate the efficacy of PET/CT when compared with other imaging methods. Researchers reviewed 151 FDG PET/CT exams that were performed on 55 children with non–central nervous system malignancies (30 patients had lymphoma—cancer that affects the body's lymph nodes and other organs that are part of the body's immune and blood-forming systems).

PET (positron emission tomography) with CT (computed tomography) imaging—with the radiotracer fluorodeoxyglucose (FDG)—enables the collection of both biological and anatomical information during a single exam, with PET picking up metabolic signals of body cells and tissues and CT offering a detailed map of internal anatomy. “PET/CT showed its broad applicability and utility by providing additional information—in more than one third of the children's exams—that could be used by doctors to more appropriately manage or treat the disease in children,” added the director of nuclear medicine/PET and vice chair of new technology and business development in the Russell H. Morgan Department of Radiology and Radiological Science. When there were discrepancies between PET/CT and conventional anatomical imaging in analyzing cancer lesions, PET/CT was diagnostically accurate 90 percent of the time, added Wahl, who pioneered the use of PET with FDG and fusion imaging in a wide range of common adult cancers.

Doctors monitor the radiation dose given to children in imaging exams, generally using lower doses than that of adult patients, to get adequate exam results, said Wahl. “Especially as a follow-up examination, PET/CT appears to be the best imaging modality currently, as it provides both PET and CT information simultaneously in pediatric patients, in whom fewer examinations are preferable,” he added. Wahl indicated that additional studies with specific childhood cancers are warranted.

PET is a powerful molecular imaging procedure that noninvasively demonstrates the function of organs and other tissues. When PET is used to image cancer, a radiopharmaceutical (such as FDG, which includes both a sugar and a radionuclide) is injected into a patient. Cancer cells metabolize sugar at higher rates than normal cells, and the radiopharmaceutical is drawn in higher amounts to cancerous areas. PET scans show where FDG is by tracking the gamma rays given off by the radionuclide tagging the drug and producing three-dimensional images of their distribution within the body. PET/CT offers precise fusion of metabolic PET images with high-quality anatomical CT images.

Besides Wahl, co-authors of “18F-FDG PET/CT in Evaluating Non-CNS Pediatric Malignancies” include Mitsuaki Tatsumi, nuclear medicine division, radiology department, and John H. Miller, pediatric radiology, radiology department, all from the Johns Hopkins Medical Institutions, Baltimore, Md.

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Co-authors of a related article note that the Johns Hopkins researchers “convincingly” show that PET/CT “may improve the evaluation and surveillance of pediatric malignancies.” Written by Noah Federman and Stephen A. Feig, the invited perspective notes, “In Hodgkin's disease and pediatric sarcomas, PET/CT appears to be an important tool in the management of these diseases. However, the use of PET/CT in other pediatric malignancies has yet to be rigorously studied.”

“PET/CT in Evaluating Pediatric Malignancies: A Clinician's Perspective” was co-written by Federman and Feig, both with Mattel Children's Hospital, David Geffen School of Medicine, University of California in Los Angeles.

Also in the Journal of Nuclear Medicine, German researchers determined that PET/CT was “significantly more accurate than PET alone for the detection and localization of lesions and improves staging of patients with Ewing tumor.” The co-authors note, “There are inherent advantages of PET/CT over PET in lesion detection, determination of malignancy and, therefore, overall staging for patients with Ewing tumor.” Ewing's tumor is a malignant bone tumor occurring in children and young adults.