Clinical performance of 68Ga-PSMA-11 PET/MRI for the detection of recurrent prostate cancer following radical prostatectomy

Sensitive visualization of recurrent prostate cancer foci is a challenge in patients with early biochemical recurrence (EBR). The recently established Ga-68-PSMA-11 PET/CT has significantly improved the detection rate with published values of up to 55% for patients with a serum PSA concentration between 0.2-0.5 ng/mL. The increased soft tissue contrast in the pelvis using simultaneous Ga-68-PSMA-11 PET/MRI might further improve the detection rate in patients with EBR and low PSA values over PET/CT. We retrospectively analyzed a cohort of 56 consecutive patients who underwent a Ga-68-PSMA-11 PET/MRI for biochemical recurrence in our institution between April and December 2016 with three readers. Median PSA level was 0.99 ng/mL (interquartile range: 3.1 ng/mL). Detection of PSMA-positive lesions within the prostate fossa, local and distant lymph nodes, bones, or visceral organs was recorded. Agreement among observers was evaluated with Fleiss's kappa (k). Overall, in 44 of 56 patients (78.6%) PSMA-positive lesions were detected. In four of nine patients (44.4%) with a PSA < 0.2 ng/mL, suspicious lesions were detected (two pelvic and one paraaortic lymph nodes, and two bone metastases). In eight of 11 patients (72.7%) with a PSA between 0.2 and < 0.5 ng/mL, suspicious lesions were detected (two local recurrences, six lymph nodes, and one bone metastasis). Five out of 20 patients with a PSA < 0.5 ng/mL had extrapelvic disease. In 12 of 15 patients (80.0%) with a PSA between 0.5 and < 2.0 ng/mL, suspicious lesions were detected (four local recurrences, nine lymph nodes, and four bone metastases). In 20 of 21 patients (95.2%) with a PSA > 2.0 ng/mL, suspicious lesions were detected. The overall interreader agreement for cancer detection was excellent (kappa = 0.796, CI 0.645-0.947). Our data show that Ga-68-PSMA-11 PET/MRI has a high detection rate for recurrent prostate cancer even at very low PSA levels < 0.5 ng/mL. Furthermore, even at those low levels extrapelvic disease can be localized in 25% of the cases and local recurrence alone is seen only in 10%.