Prospective Head-to-Head Comparison of 18F-PSMA PET/CT and 18F-NaF PET/CT for Assessing Bone Metastases in 160 Patients with Newly Diagnosed High-Risk Prostate Cancer

Abstract

Prostate-specific membrane antigen (PSMA) PET/CT is increasingly used for primary staging in prostate cancer (PC), mainly because of its improved accuracy in detecting lymph node metastases compared with conventional imaging. However, the diagnostic benefit of PSMA PET/CT for detecting bone metastases is less well established. This study compares the diagnostic accuracy of ¹⁸F-PSMA PET/CT and ¹⁸F-NaF PET/CT for detecting bone metastases in patients newly diagnosed with PC. Methods: This prospective study included patients with histologically confirmed high-risk PC. All participants were referred from the department of urology to ¹⁸F-NaF PET/CT and underwent ¹⁸F-PSMA PET/CT within 3 weeks. Images were reviewed by 2 nuclear medicine physicians unaware of the results of the other imaging modality. Presence or absence of bone metastases and number of metastatic lesions were recorded. A reference standard was established at the patient level based on agreement between the 2 imaging modalities. In cases of concordance, both modalities were deemed correct. In cases of discordance, additional follow-up scans were performed. Diagnostic performance metrics, including sensitivity, specificity, and accuracy, were calculated. Results: In total, 160 participants were included. Sensitivity, specificity, and accuracy for detecting bone metastases at the patient level were 0.98, 0.99, and 0.99, respectively, for ¹⁸F-PSMA PET/CT, and 0.91, 1.00, and 0.97, respectively, for ¹⁸F-NaF PET/CT. No significant differences were found. The concordance rate of bone metastases between ¹⁸F-NaF and ¹⁸F-PSMA PET/CT at the patient level was observed in 154 patients (96.3%). ¹⁸F-PSMA PET/CT tended to identify more bone metastases per patient than ¹⁸F-NaF PET/CT. Conclusion: Both ¹⁸F-NaF and ¹⁸F-PSMA PET/CT exhibit high diagnostic accuracy for detecting bone metastases in newly diagnosed high-risk PC patients. ¹⁸F-PSMA PET/CT may detect additional metastatic lesions compared with ¹⁸F-NaF PET/CT. Subsequent ¹⁸F-NaF PET/CT may be redundant if no bone metastases are found on ¹⁸F-PSMA PET/CT.

Keywords: NaF PET/CT; PSMA PET/CT; bone metastases; diagnostic accuracy; prostate cancer.

Graphical abstract

FIGURE 1.

Flowchart illustrating process of achieving final diagnosis of bone metastases on patient level.

FIGURE 2.

Flowchart illustrating inclusion process of study participants.

FIGURE 3.

Patient with discordant findings on baseline ¹⁸F-NaF and ¹⁸F-PSMA PET/CT. (A) Maximum-intensity projection and axial projection of ¹⁸F-NaF PET/CT scan with no evidence of bone metastases. (B) ¹⁸F-PSMA PET/CT scan showing 2 lesions, one in left ilium and another in right costa 6, which were suspected of being bone metastases (red arrows). Third faint lesion in right ilium was not interpreted as bone metastasis (green arrows). Because of absence of metastatic lesions on ¹⁸F-NaF PET/CT (conventional scan), patient was observed, without treatment. (C and D) Follow-up scans conducted 6 months later revealed detectable uptake in lesion in right ilium on ¹⁸F-NaF PET/CT and increasing uptake on ¹⁸F-PSMA PET/CT (orange arrows). There are multiple ¹⁸F-PSMA-avid lymph nodes on follow-up scan.

FIGURE 4.

Sankey diagram of number of bone metastases detected by ¹⁸F-NaF PET/CT and ¹⁸F-PSMA PET/CT in 44 patients with bone metastases according to reference standard. bm = bone metastases.