Total-Body ⁶⁸Ga-PSMA-11 PET/CT for Bone Metastasis Detection in Prostate Cancer Patients: Potential Impact on Bone Scan Guidelines

Our purpose was to determine the relationship between serum prostate-specific antigen (PSA) level categories (<5, 5-10, 10-20, and >20 ng/mL) and the incidence of bone metastases detected by total-body ⁶⁸Ga-prostate-specific membrane antigen (PSMA)-11 PET/CT and to assess if expanding the ⁶⁸Ga-PSMA-11 PET/CT imaging field to include the vertex and lower extremities (total-body acquisition) affects bone metastasis detection rates and patient management. Methods: This was a retrospective analysis of 388 prostate cancer patients enrolled in 5 prospective studies (NCT02940262, NCT03368547, NCT03042312, NCT04050215, and NCT03515577). All underwent ⁶⁸Ga-PSMA-11 PET/CT scans acquired from vertex to toes for primary staging (n = 93/388, 24%), biochemical recurrence (BCR) localization (n = 225/388, 58%), or restaging metastatic disease (M1) before or during systemic therapy (n = 70/388, 18%) between September 2017 and May 2018. Results: In total, 321 of 388 patients (83%) had a positive ⁶⁸Ga-PSMA-11 study. PSMA-positive bone lesions were found in 105 of 388 (27%) patients, with an incidence that was positively associated with serum PSA level (<10 ng/mL, 21%; 10-20 ng/mL, 41%; ≥20 ng/mL, 41%; P < 0.001). This association was maintained for all 3 indications: initial staging, BCR, and restaging M1. Bone metastases occurred most frequently in restaging M1, followed by BCR and initial staging. Bone metastasis incidence was not significantly associated with National Comprehensive Cancer Network risk score (P = 0.22). The average number of PSMA-positive regions also increased with serum PSA level (P < 0.001). Eighteen of 388 (5%) and 18 of 388 (5%) had lesions above the superior orbital ridge and below the proximal third of the femur, respectively. There was only 1 of 388 patients (0.26%) in whom the total-body PET acquisition had an impact on management. Conclusion: Bone metastases as assessed with ⁶⁸Ga-PSMA-11 PET/CT are prevalent even in patients with low serum PSA levels. Therefore, current guidelines for bone assessments in prostate cancer patients should be revisited because ⁶⁸Ga-PSMA-11 PET/CT may provide additional information for accurate bone staging at low serum PSA levels. Including the total body (from vertex to toes) in ⁶⁸Ga-PSMA-11 PET/CT imaging revealed additional bone lesions in 6% of patients, but without significantly affecting patient management.