Comparison between Ga-PSMA-11 PET/CT and multiparametric magnetic resonance imaging in patients with biochemically recurrent prostate cancer following robot-assisted radical prostatectomy.

Background/purpose: We sought to compare the diagnostic performances of Ga-PSMA-11 PET/CT and prostate/whole-abdomen multiparametric magnetic resonance imaging (PWAmpMRI) in Taiwanese patients with biochemically recurrent prostate cancer following robot-assisted radical prostatectomy.

Methods: Between June 2017 and December 2018, we prospectively enrolled 34 patients. Upon review of all available clinical and imaging data, a best valuable comparator (BVC) was defined on an individual basis in the light of a consensus reached by a multidisciplinary tumor board. Diagnostic positivity was investigated in relation to the different lesion types.

Results: On a patient-based analysis, Ga-PSMA-11 PET/CT and PWAmpMRI showed a moderate agreement (kappa coefficient = 0.62). Ga-PSMA-11 PET/CT identified local recurrences, regional, and non-regional lymph node metastases, and bone metastases in 15, 10, 1, and 5 patients, respectively. Conversely, PWAmpMRI detected these lesions in 26, 8, 1, and 4 patients, respectively. When the BVC was used as reference standard, the positive diagnostic rates for local recurrences, regional lymph node metastases, non-regional lymph node metastases, and bone metastases were 57.7%, 90.9%, 100%, and 100%, respectively for Ga-PSMA-11 PET/CT, and 100%, 72.7%, 100%, and 80% for PWAmpMRI, respectively. The use of both PWAmpMRI and Ga-PSMA-11 PET/CT showed a complete diagnostic yield for detecting both local recurrence and systemic failure when PSA levels reached 0.5 ng/mL.

Conclusion: Due to urine radioactivity, Ga-PSMA-11 PET/CT performs less than PWAmpMRI on local recurrences. However, it can have a complementary diagnostic role in the detection of lymph node metastases and in identifying non-axial bone metastases beyond the PWAmpMRI scanning field.