68 Ga-PSMA and 68 Ga-DOTA-RM2 PET/MRI in Recurrent Prostate Cancer: Diagnostic Performance and Association with Clinical and Histopathological Data

The aim of the present study is to investigate and compare the performances of Ga-PSMA and Ga-DOTA-RM2 PET/MRI in identifying recurrent prostate cancer (PCa) after primary treatment and to explore the association of dual-tracer PET findings with clinical and histopathological characteristics. Thirty-five patients with biochemical relapse (BCR) of PCa underwent Ga PSMA PET/MRI for restaging purpose, with 31/35 also undergoing Ga-DOTA-RM2 PET/MRI scan within 16 days (mean: 3 days, range: 2-16 days). Qualitative and quantitative image analysis has been performed by comparing Ga-PSMA and Ga-DOTA-RM2 PET/MRI findings both on a patient and lesion basis. Clinical and instrumental follow-up was used to validate PET findings. Fisher's exact test and Mann-Whitney U test were used to investigate the association between dual-tracer PET findings, clinical and histopathological data. -value significance was defined below the 0.05 level. Patients' mean age was 70 years (range: 49-84) and mean PSA at time of PET/MR scans was 1.88 ng/mL (range: 0.21-14.4). A higher detection rate was observed for Ga-PSMA PET/MRI, with more lesions being detected compared to Ga-DOTA-RM2 PET/MRI (26/35 patients, 95 lesions vs. 15/31 patients, 41 lesions; = 0.016 and 0.002). Ga-PSMA and Ga-DOTA-RM2 PET/MRI findings were discordant in 11/31 patients; among these, 10 were Ga-PSMA positive (9/10 confirmed as true positive and 1/10 as false positive by follow-up examination). Patients with higher levels of PSA and shorter PSA doubling time (DT) presented more lesions on Ga-PSMA PET/MRI ( = 0.006 and 0.044), while no association was found between PET findings and Gleason score. Ga-PSMA has a higher detection rate than Ga-DOTA-RM2 in detecting PCa recurrence. The number of Ga-PSMA PET positive lesions is associated with higher levels of PSA and shorter PSA DT, thus representing potential prognostic factors.