Prospective Comparison of Ga-NeoB and Ga-PSMA-R2 PET/MRI in Patients with Biochemically Recurrent Prostate Cancer.

Prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptors are both overexpressed in prostate cancer (PC) but may provide complementary information.Ga-PSMA-R2 and Ga-NeoB (DOTA--aminomethylaniline-diglycolic acid-DPhe-Gln-Trp-Ala-Val-Gly-His-NH-CH[CH-CH(CH)]) are novel PET radiopharmaceuticals that were developed for theranostic use. In this phase II imaging study, we assessed the feasibility, safety, and diagnostic performance of Ga-NeoB and Ga-PSMA-R2 PET/MRI for detection of biochemically recurrent PC. We prospectively enrolled 27 men with suspected biochemically recurrent PC after initial treatment but noncontributory conventional imaging results (negative or equivocal findings on MRI, CT, and/or bone scan). Participants underwent Ga-NeoB and Ga-PSMA-R2 PET/MRI within 2 wk in noncontrolled order. The SUV of putative PC lesions was measured and compared with a composite reference standard (histopathology, follow-up imaging, prostate-specific antigen change). The SUV and SUV of background organs were measured. Vital signs were recorded before injection of the radiopharmaceuticals and after the scans. Adverse events were recorded up to 72 h after each scan. The prostate-specific antigen level at enrollment was 3.5 ± 3.9 ng/mL (range, 0.3-13.5 ng/mL). Ga-NeoB PET/MRI detected 31 lesions in 18 patients (66.7%), whereas Ga-PSMA-R2 identified 20 lesions in 15 participants (55.6%). Ga-NeoB PET/MRI showed higher sensitivity (85.7% vs. 71.4%), accuracy (88.9% vs. 77.8%), and negative predictive value (66.7% vs. 50.0%) than Ga-PSMA-R2, whereas specificity and positive predictive value were equally high (100.0% for both). In 6 patients, Ga-NeoB PET/MRI identified 14 lesions that were false-negative on Ga-PSMA-R2 PET/MRI. The mean lesion SUV was 6.6 ± 3.2 (range, 2.9-13.2) for Ga-NeoB and 4.4 ± 1.5 (range, 2.6-8.8) for Ga-PSMA-R2 ( = 0.019). Overall lower uptake was noted in tumors and background organs for Ga-PSMA-R2. There were no significant changes in vital signs before and after the scans. No adverse events were reported in the 72-h period after scans. Ga-NeoB and Ga-PSMA-R2 are safe for diagnostic imaging. Ga-NeoB PET/MRI showed better diagnostic performance than Ga-PSMA-R2. Ga-PSMA-R2 showed overall lower uptake, equally in background organs and tumors, and might therefore not be an ideal theranostic compound. Further evaluation in larger cohorts is needed to confirm our preliminary data.