Comparison of NaF and FDG PET/CT for Assessment of Treatment Response in Castration-Resistant Prostate Cancers With Osseous Metastases

This article compares pharmacodynamic responses of skeletal metastases to therapy. Patients with skeletal metastases had multiple dynamic NaF/FDG PET scans, providing uptake (SUV and K-i) and vascular (K-1 and V-b) responses. Late responses were consistently correlated, but earlier uptake responses and all vasculature responses were different. Although some NaF and FDG PET treatment responses are related, using both tracers provides additional information. Background: Assessment of skeletal metastases' response to therapy is a highly relevant but unresolved clinical problem. The main goal of this work was to compare pharmacodynamic responses to therapy assessed with positron emission tomographyecomputed tomography (PET/CT) using fluorine-18 sodium fluoride (NaF) and fluorine-18 fluorodeoxyglucose (FDG) as the tracers. Materials and Methods: Patients with prostate cancer with known osseous metastases were treated with zibotentan (ZD4054) and imaged with combined dynamic NaF/FDG PET/CT before therapy (baseline), after 4 weeks of therapy (week 4), and after 2 weeks of treatment break (week 6). Kinetic analysis allowed comparison of the voxel-based tracer uptake rate parameter Ki, the vasculature parameters K1 (measuring perfusion/permeability) and Vb (measuring vasculature fraction in the tissue), and the standardized uptake values (SUVs). Results: Correlations were high for the NaF and FDG peak uptake parameters (Ki and SUV correlations ranged from 0.57 to 0.88) and for vasculature parameters (K1 and Vb correlations ranged from 0.61 to 0.81). Correlation was low between the NaF and FDG week 4 Ki responses (rho = 0.35; P = .084) but was higher for NaF and FDG week 6 Ki responses (rho = 0.72; P < .0001). Correlations for vasculature responses were always low (r < 0.35). NaF and FDG uptakes in the osseous metastases were spatially dislocated, with overlap in the range from 0% to 80%. Conclusion: This study found that late NaF and FDG uptake responses are consistently correlated but that earlier uptake responses and all vasculature responses can be unrelated. This study also confirmed that FDG and NaF uptakes are spatially dislocated. Although treatment responses assessed with NaF and FDG may be correlated, using both tracers provides additional information.