Prospective comparison of combined 18F-FDG and 18F-NaF PET/CT vs. 18F-FDG PET/CT imaging for detection of malignancy

Purpose Typically, F-18-FDG PET/CT and F-18-NaF PET/CT scans are done as two separate studies on different days to allow sufficient time for the radiopharmaceutical from the first study to decay. This is inconvenient for the patients and exposes them to two doses of radiation from the CT component of the examinations. In the current study, we compared the clinical usefulness of a combined F-18-FDG/F-18-NaF PET/CT scan with that of a separate F-18-FDG-only PET/CT scan. Methods There were 62 patients enrolled in this prospective trial. All had both an F-18-FDG-alone PET/CT scan and a combined 18F-FDG/F-18-NaF PET/CT scan. Of the 62 patients, 53 (85%) received simultaneous tracer injections, while 9 (15%) received 18F-NaF subsequent to the initial F-18-FDG dose (average delay 2.2 h). Images were independently reviewed for PET findings by two Board-Certified nuclear medicine physicians, with discrepancies resolved by a third reader. Interpreters were instructed to only report findings that were concerning for malignancy. Reading the F-18-FDG-only scan first for half of the patients controlled for order bias. Results In 15 of the 62 patients (24%) neither the F-18-FDG-only PET/CT scan nor the combined F-18-FDG/F-18-NaF PET/CT scan identified malignancy. In the remaining 47 patients who had PET findings of malignancy, a greater number of lesions were detected in 16 of 47 patients (34%) using the combined F-18-FDG/F-18-NaF PET/CT scan compared to the F-18-FDG-only PET/CT scan. In 2 of these 47 patients (4%), the F-18-FDG-only scan demonstrated soft tissue lesions that were not prospectively identified on the combined study. In 29 of these 47 patients (62%), the combined scan detected an equal number of lesions compared to the 18F-FDG-only scan. Overall, 60 of all the 62 patients (97%) showed an equal or greater number of lesions on the combined scan than on the F-18-FDG-only scan. Conclusion The current study demonstrated that 18F-FDG and F-18-NaF can be combined in a single PET/CT scan by administering the two radiopharmaceuticals simultaneously or in sequence on the same day. In addition to patient convenience and reduced radiation exposure from the CT component, the combined F-18-FDG/F-18-NaF PET/CT scan appeared to increase the sensitivity for detection of osseous lesions compared to the F-18-FDG-only PET/CT scan in the studied population.