PET/CT studies of multiple myeloma using 18F-FDG and 18F-NaF: comparison of distribution patterns and tracers' pharmacokinetics

Objective The aim of this prospective study is to evaluate the combined use of fluorine-18 fluorodeoxyglucose ((18) F-FDG) and fluorine-18 sodium fluoride ((18) F-NaF) PET/CT in the skeletal assessment of patients with multiple myeloma (MM) and to compare the efficacy of these two PET tracers regarding detection of myeloma-indicative osseous lesions. Patients and methods The study includes 60 patients with multiple myeloma (MM) diagnosed according to standard criteria. All patients underwent dynamic (dPET/CT) scanning of the pelvis as well as whole body PET/CT studies with both tracers. The interval between the two exams was one day. Sites of focal increased (18) F-FDG uptake were considered as highly suspicious of myelomatous involvement. The lesions detected on the (18) F-NaF PET/CT scans were then correlated with those detected on (18) F-FDG PET/CT, which served as a reference. Moreover, the (18) F-FDG PET/CT results were also correlated with the low-dose CT findings. The evaluation of dPET/CT studies was based on qualitative evaluation, SUV calculation, and quantitative analysis based on a 2-tissue compartment model and a non-compartmental approach. Results Whole body (18) F-FDG PET/CT revealed approximately 343 focal lesions while (18) F-NaF PET/CT revealed 135 MM-indicative lesions (39 % correlation). CT demonstrated 150 lesions that correlated with those in (18) F-FDG PET/CT (44 % correlation). Six patients demonstrated a diffuse pattern of disease with (18) F-FDG, while 15 of them had a mixed (diffuse and focal) pattern of skeletal (18) F-FDG uptake. A high number of degenerative, traumatic and arthritic disease lesions were detected with (18) F-NaF PET/CT. In three patients with multiple focal (18) F-FDG-uptake, (18) F-NaF PET/CT failed to demonstrate any bone lesion. The dPET/CT scanning of the pelvic area with (18) F-FDG and (18) F-NaF revealed 77 and 24 MM-indicative lesions, respectively. Kinetic analysis of (18) F-FDG revealed the following mean values: SUVaver = 5.1, k(1) = 0.37 (1/min), k(3) = 0.10 (1/min), V-B = 0.06, influx = 0.04 (1/min), FD = 1.28; the respective values for (18) F-NaF were SUVaverage = 10.7, k(1) = 0.25 (1/min), k(3) = 0.34 (1/min), V-B = 0.02, influx = 0.10 (1/min), FD = 1.37. Apart from the correlation between V-B of (18) F-FDG and k(1) of (18) F-NaF (r = 0.54), no other significant correlation was observed between the two tracers' kinetic parameters. We found a significant correlation between FD and SUVaverage (r = 0.93), FD and SUVmax (r = 0.80), FD and influx ( r = 0.85), as well as between influx and SUVaverage (r = 0.74) for (18) F-FDG. In (18) F-NaF we observed the most significant correlations between FD and SUVaverage (r = 0.97), FD and SUVmax (r = 0.87), and between influx and k(1) (r = 0.72). Conclusion The combined use of (18) F-FDG PET/CT and (18) F-NaF PET/CT provides different molecular information regarding the biological processes that take place in a MM osseous lesion. (18) F-FDG PET/CT proved to be a more specific biomarker than (18) F-NaF PET/CT in multiple myeloma skeletal assessment.