A comparison of prostate cancer bone metastases on 18 F-Sodium Fluoride and Prostate Specific Membrane Antigen ( 18 F-PSMA) PET/CT: Discordant uptake in the same lesion.

Purpose: Prostate-Specific Membrane Antigen (PSMA) PET/CT has been introduced as a sensitive method for characterizing metastatic prostate cancer. The purpose of this study is to compare the spatial concordance of 18 F-NaF PET/CT and 18 F-PSMA-targeted PET/CT within prostate cancer bone metastases.

Methods: Prostate cancer patients with known bone metastases underwent PSMA-targeted PET/CT (18 F-DCFBC or 18 F-DCFPyL) and 18 F-NaF PET/CT. In pelvic and spinal lesions detected by both radiotracers, regions-of-interest (ROIs) derived by various thresholds of uptake intensity were compared for spatial colocalization. Overlap volume was correlated with uptake characteristics and disease status.

Results: The study included 149 lesions in 19 patients. Qualitatively, lesions exhibited a heterogeneous range of spatial concordance between PSMA and NaF uptake from completely matched to completely discordant. Quantitatively, overlap volume decreased as a function of tracer intensity. and disease status, where lesions from patients with castration-sensitive disease showed higher spatial concordance while lesions from patients with castration-resistant disease demonstrated more frequent spatial discordance.

Conclusion: As metastatic prostate cancer progresses from castration-sensitive to castration-resistant, greater discordance is observed between NaF PET and PSMA PET uptake. This may indicate a possible phenotypic shift to tumor growth that is more independent of bone remodeling via osteoblastic formation.