Optimizing an 18F-NaF and 18F-FDG cocktail for PET assessment of metastatic castration-resistant prostate cancer

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Abstract

Background

PET/computed tomography (CT) imaging with the sodium-(18F)-fluoride/2-(18F)-fluoro-2-deoxy-D-glucose (18F-NaF/18F-FDG) cocktail has been proposed for patients with osseous metastases. This work aimed to optimize the cocktail composition for patients with metastatic castration-resistant prostate cancer (mCRPC).

Materials and methods

The study was carried out on six patients with mCRPC, with a total of 26 analyzed lesions. The patients were injected with 18F-NaF and 18F-FDG at separate time points. Dynamic PET/CT imaging recorded the uptake time course for both the tracers into osseous metastases. 18F-NaF and 18F-FDG uptakes were decoupled by kinetic analysis, which enabled calculation of 18F-NaF and 18F-FDG standardized uptake values (SUVs) images. Peak, mean, and total SUVs were evaluated for both tracers and all visible lesions. The 18F-NaF/18F-FDG cocktail was optimized under the assumption that the contribution of both tracers to image formation is equal. SUV images from PET/CT imaging with a combination of 18F-NaF and 18F-FDG were generated for cocktail compositions with an 18F-NaF : 18F-FDG ratio varying from 1 : 8 to 1 : 2.

Results

The 18F-NaF peak and mean SUVs were on average four to five times higher than the 18F-FDG peak and mean SUVs, with an interlesion coefficient of variations of 20%. The total SUV for 18F-NaF was on average seven times higher than that for 18F-FDG. When the 18F-NaF : 18F-FDG ratio changed from 1 : 8 to 1 : 2, the typical SUV on the generated PET images increased by 50%, whereas the change in the uptake visual pattern was hardly noticeable.

Conclusion

18F-NaF and 18F-FDG in the cocktail contribute equally to image formation when the 18F-NaF : 18F-FDG ratio is 1 : 5. Therefore, we propose this ratio as the optimal cocktail composition for mCRPC patients. We also urge to strictly control the cocktail composition during any 18F-NaF/18F-FDG cocktail PET/CT examination.

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