TORONTO, CanadaPositron emission tomography (PET) proved superior to both CT and MRI for both diagnosis and therapeutic monitoring of pediatric cancer patients in a study conducted at the University of Munich. Ute Porn, Jr., MD, described the results at the 48th Annual Meeting of the Society of Nuclear Medicine (abstract 144).
PET assesses the rate of cellular metabolism in tumors by determining the rate of uptake of radiolabeled fluorodeoxyglucose (FDG), an analog of glucose. In PET scans, cancerous tumors show up more brightly than noncancerous tissues. This selectivity, indicative of a higher rate of glucose usage, reflects the fact that cancer cells usually have a higher metabolic rate than nonmalignant cells.
Dr. Porn and her colleagues examined a total of 63 PET scans in 42 children, aged 1 to 17, with known or suspected tumors. Diagnoses from the imaging techniques were then confirmed by histopathology, clinical follow-up, or both.
While all the patients had cancer at some point, in this study some were investigated after chemotherapy/radiotherapy and/or surgery, so that in many instances no recurrent tumor would have been expected.
Overall, PET proved equal to or better than the other imaging techniques in both sensitivity and specificity, and was especially superior in specificity, ie, in avoiding diagnoses of cancer where none was present.
Moreover, in discussing the results, Dr. Porn indicated that PET was also better than CT or MRI in delineating scar tissue from residual tumors, and showed good correlation between post-therapeutic radioactive uptake and response of the tumor to treatment.
The one false-positive PET reading reflected enhanced FDG uptake by muscle, a tissue known to be highly active metabolically, while the false-negative readings resulted either from particularly small tumors or from tumors whose glucose metabolism proved to be lower than is typically observed in cancerous cells.