Diagnostic Accuracy of Fully Hybrid [Ga]Ga-PSMA-11 PET/MRI and [Ga]Ga-RM2 PET/MRI in Patients with Biochemically Recurrent Prostate Cancer: a Prospective Single-center Phase II Clinical Trial

Purpose: To compare the diagnostic accuracy and detection rates of PET/MRI with [Ga]Ga-PSMA-11 and [Ga]Ga-M2 in patients with biochemical recurrence of prostate cancer (PCa).

Methods: Sixty patients were enrolled in this prospective single-center phase II clinical trial from June 2020 to October 2022. Forty-four/60 completed all study examinations and were available at follow-up (median: 22.8 months, range: 6-31.5 months). Two nuclear medicine physicians analyzed PET images and two radiologists interpreted MRI; images were then re-examined to produce an integrated PET/MRI report for both [Ga]Ga-PSMA-11 and [Ga]Ga-RM2 examinations. A composite reference standard including histological specimens, response to treatment, and conventional imaging gathered during follow-up was used to validate imaging findings. Detection rates, accuracy, sensitivity, specificity, positive, and negative predictive value were assessed. McNemar's test was used to compare sensitivity and specificity on a per-patient base and detection rate on a per-region base. Prostate bed, locoregional lymph nodes, non-skeletal distant metastases, and bone metastases were considered. p-value significance was defined below the 0.05 level after correction for multiple testing.

Results: Patients' median age was 69.8 years (interquartile range (IQR): 61.8-75.1) and median PSA level at time of imaging was 0.53 ng/mL (IQR: 0.33-2.04). During follow-up, evidence of recurrence was observed in 31/44 patients. Combining MRI with [Ga]Ga-PSMA-11 PET and [Ga]Ga-RM2 PET resulted in sensitivity = 100% and 93.5% and specificity of 69.2% and 69.2%, respectively. When considering the individual imaging modalities, [Ga]Ga-RM2 PET showed lower sensitivity compared to [Ga]Ga-PSMA-11 PET and MRI (61.3% vs 83.9% and 87.1%, p = 0.046 and 0.043, respectively), while specificity was comparable among the imaging modalities (100% vs 84.6% and 69.2%, p = 0.479 and 0.134, respectively).

Conclusion: This study brings further evidence on the utility of fully hybrid PET/MRI for disease characterization in patients with biochemically recurrent PCa. Imaging with [Ga]Ga-PSMA-11 PET showed high sensitivity, while the utility of [Ga]Ga-RM2 PET in absence of a simultaneous whole-body/multiparametric MRI remains to be determined.