Determination of the optimal imaging protocol for [18F]PSMA-PET-CT for the detection of bone metastases in prostate cancer patients.

Aim: Prostate-specific membrane antigen-positron emission tomography (PSMA-PET) is a widely used diagnostic tool in patients with prostate cancer (PC). However, due to the limited availability of PET scanners and relevant acquisition costs, it is important to consider the indications and acquisition time. The aim of this investigation was to determine whether a PET scan from the skull base to the proximal thigh is sufficient to detect the presence of bone metastases.

Methods: A retrospective analysis was conducted on 1050 consecutive [¹⁸F]PSMA-1007-PET-CT scans from the head to the proximal lower leg. The PET scans were categorised according to the presence and amount of bone metastases: (1) 1-5, (2) 6-19 and (3) ≥20. Additionally, the PET scans were evaluated for the presence of bone metastases below the proximal thigh as well as bone metastases above the skull base. Imaging results were compared to patients PSA values.

Results: Of the 391 patients with bone metastases, 146 (37.3%) exhibited metastases located below the proximal thigh and 104 (26.6%) above the skull base. The majority of bone metastases located below the proximal thigh (145, 99.3%) and above the skull base (94, 90.4%) were identified in patients with more than five bone metastases. No solitary distal metastasis was detected. The PSA value correlated significantly with number of bone metastases (e. g., 1-5 vs. ≥20 bone metastases, P < 0.001) and was significantly higher in patients with distal bone metastases (P < 0.001). ROC analysis showed that a PSA value of 11.15 ng/mL is the optimal cut-off for detecting bone metastases located below the proximal thigh, with an AUC of 0.919 (95% CI: 0.892-0.945, sensitivity 87%, specificity 86%). Similarly, the PSA value of 12.86 ng/mL is the optimal cut-off for detecting bone metastases above the skull base with an AUC of 0.904 (95% CI: 0.874-0.935, sensitivity 87%, specificity 83%).  CONCLUSION: PSMA-PET acquisition protocols from the skull base to the proximal femur may be sufficient to accurately detect bone metastatic disease in PC. PSA values can provide decision support for individual PET acquisition protocols.