Comparison of [68Ga]Ga-PSMA-11 PET/CT with [18F]NaF PET/CT in the evaluation of bone metastases in metastatic prostate cancer patients prior to radionuclide therapy

AimThe purpose of this study was to investigate the diagnostic performance of Ga-68-PSMA-11 PET/CT in the evaluation of bone metastases in metastatic prostate cancer (PC) patients scheduled for radionuclide therapy in comparison to [F-18]sodium fluoride (F-18-NaF) PET/CT.MethodsSixteen metastatic PC patients with known skeletal metastases, who underwent both Ga-68-PSMA-11 PET/CT and F-18-NaF PET/CT for assessment of metastatic burden prior to radionuclide therapy, were analysed retrospectively. The performance of both tracers was calculated on a lesion-based comparison. Intensity of tracer accumulation of pathologic bone lesions on F-18-NaF PET and Ga-68-PSMA-11 PET was measured with maximum standardized uptake values (SUVmax) and compared to background activity of normal bone. In addition, SUVmax values of PET-positive bone lesions were analysed with respect to morphologic characteristics on CT. Bone metastases were either confirmed by CT or follow-up PET scan.ResultsIn contrast to 468 PET-positive lesions suggestive of bone metastases on F-18-NaF PET, only 351 of the lesions were also judged positive on Ga-68-PSMA-11 PET (75.0%). Intensity of tracer accumulation of pathologic skeletal lesions was significantly higher on F-18-NaF PET compared to Ga-68-PSMA-11 PET, showing a median SUVmax of 27.0 and 6.0, respectively (p<0.001). Background activity of normal bone was lower on Ga-68-PSMA-11 PET, with a median SUVmax of 1.0 in comparison to 2.7 on F-18-NaF PET; however, tumour to background ratio was significantly higher on F-18-NaF PET (9.8 versus 5.9 on Ga-68-PSMA-11 PET; p=0.042). Based on morphologic lesion characterisation on CT, F-18-NaF PET revealed median SUVmax values of 23.6 for osteosclerotic, 35.0 for osteolytic, and 19.0 for lesions not visible on CT, whereas on Ga-68-PSMA-11 PET median SUVmax values of 5.0 in osteosclerotic, 29.5 in osteolytic, and 7.5 in lesions not seen on CT were measured. Intensity of tracer accumulation between(18)F-NaF PET and Ga-68-PSMA-11 PET was significantly higher in osteosclerotic (p<0.001) and lesions not visible on CT (p=0.012).ConclusionIn comparison to Ga-68-PSMA-11 PET/CT, F-18-NaF PET/CT detects a higher number of pathologic bone lesions in advanced stage PC patients scheduled for radionuclide therapy. Our data suggest that Ga-68-PSMA-11 PET should be combined with F-18-NaF PET in PC patients with skeletal metastases for restaging prior to initiation or modification of therapy.