Intra‐individual comparison of prostate‐specific membrane antigen positron emission tomography/computed tomography versus bone scan in detecting skeletal metastasis at prostate cancer diagnosis

Objectives To compare the diagnostic performance and radiological staging impact of 68 Ga‐prostate‐specific membrane antigen positron emission tomography/computed tomography (PSMA PET/CT) compared to 99 Tc whole‐body bone scan (WBBS) for the detection of skeletal metastasis in the primary staging of prostate cancer (PCa). Patients and Methods A prospective institutional database was retrospectively examined for patients who underwent both PSMA PET and WBBS within a 1 week interval for PCa primary staging. Lesions were categorised as ‘negative’, ‘equivocal’, or ‘definite’ based on nuclear medicine physician interpretation. Metastatic burden was characterised for each imaging modality according to three groups: (i) local disease (no skeletal metastases), (ii) oligometastatic disease (three or fewer skeletal metastases), or (iii) polymetastatic disease (more than three skeletal metastases). Results There were 667 patients included. The median (interquartile range) prostate‐specific antigen level was 9.2 (6.2–16) ng/mL and 60% of patients were high risk according to a modified D'Amico risk classification. The overall distribution of skeletal metastasis detection changed across the two scans overall ( P = 0.003), being maintained within high‐risk ( P = 0.030) and low‐risk ( P = 0.018) groups. PSMA PET/CT identified more definite skeletal metastases compared to WBBS overall (10.3% vs 7.3%), and according to risk grouping (high: 12% vs 9%, intermediate: 4% vs 1%). Upstaging was more common with PSMA PET/CT than WBBS ( P = 0.001). The maximum standardised uptake value (SUV max ) of the primary tumour was associated with upstaging of skeletal metastases on PSMA PET/CT ( P = 0.025), while age was associated with upstaging on WBBS ( P = 0.021). The SUV max of the primary tumour and metastases were both higher according to extent of metastatic disease ( P = 0.001 and P < 0.001, respectively). Conclusions More skeletal metastases were detected with PSMA PET/CT than WBBS, resulting in a higher upstaging rate mostly in high‐risk patients. The SUV max of the primary tumour and metastases was associated with upstaging.