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

Aim: The purpose of this study was to investigate the diagnostic performance of ⁶⁸ Ga-PSMA-11 PET/CT in the evaluation of bone metastases in metastatic prostate cancer (PC) patients scheduled for radionuclide therapy in comparison to [ ¹⁸ F]sodium fluoride ( ¹⁸ F-NaF) PET/CT.
Methods: Sixteen metastatic PC patients with known skeletal metastases, who underwent both ⁶⁸ Ga-PSMA-11 PET/CT and ¹⁸ F-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 ¹⁸ F-NaF PET and ⁶⁸ Ga-PSMA-11 PET was measured with maximum standardized uptake values (SUV _max ) and compared to background activity of normal bone. In addition, SUV _max 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.
Results: In contrast to 468 PET-positive lesions suggestive of bone metastases on ¹⁸ F-NaF PET, only 351 of the lesions were also judged positive on ⁶⁸ Ga-PSMA-11 PET (75.0%). Intensity of tracer accumulation of pathologic skeletal lesions was significantly higher on ¹⁸ F-NaF PET compared to ⁶⁸ Ga-PSMA-11 PET, showing a median SUV _max of 27.0 and 6.0, respectively (p < 0.001). Background activity of normal bone was lower on ⁶⁸ Ga-PSMA-11 PET, with a median SUV _max of 1.0 in comparison to 2.7 on ¹⁸ F-NaF PET; however, tumour to background ratio was significantly higher on ¹⁸ F-NaF PET (9.8 versus 5.9 on ⁶⁸ Ga-PSMA-11 PET; p = 0.042). Based on morphologic lesion characterisation on CT, ¹⁸ F-NaF PET revealed median SUV _max values of 23.6 for osteosclerotic, 35.0 for osteolytic, and 19.0 for lesions not visible on CT, whereas on ⁶⁸ Ga-PSMA-11 PET median SUV _max 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 ⁶⁸ Ga-PSMA-11 PET was significantly higher in osteosclerotic (p < 0.001) and lesions not visible on CT (p = 0.012).
Conclusion: In comparison to ⁶⁸ Ga-PSMA-11 PET/CT, ¹⁸ F-NaF PET/CT detects a higher number of pathologic bone lesions in advanced stage PC patients scheduled for radionuclide therapy. Our data suggest that ⁶⁸ Ga-PSMA-11 PET should be combined with ¹⁸ F-NaF PET in PC patients with skeletal metastases for restaging prior to initiation or modification of therapy.