Prospective evaluation of 68Ga-RM2 PET/MRI and 68Ga-PSMA11 PET/CT in patients with biochemical recurrence of prostate cancer

589 Objectives: Early diagnosis of biochemically recurrent prostate cancer (BCR PC) after primary treatments remains a challenge; however, new prostate cancer specific radioligands have been developed and early results are encouraging. Here, we compare the gastrin releasing peptide receptors (GRPRs) - targeting 68Ga-RM2 and the prostate specific membrane antigen (PSMA) - targeting 68Ga-PSMA11. Materials and Methods: We prospectively enrolled 29 patients, 60 - 83 year-old (mean±Standard Deviation (SD): 71.34±5.73), who had both 68Ga-RM2 PET/MRI and 68Ga-PSMA11 PET/CT. 68Ga-RM2 imaging started 45.1 - 91 minutes (mean±SD: 55.84±11.01) after injection of 3.7 - 4.2 mCi (mean±SD: 3.98±0.13) using a TOF-enabled, SiPM-based, simultaneous PET/MRI scanner. 68Ga-PSMA11 imaging started at 45 - 107.9 minutes (mean±SD: 67.31±15.10) after injection of 3.5 - 5.4 mCi (mean±SD: 4.03±0.35) using a SiPM-based PET/CT scanner. The standardized uptake value (SUVmax) was collected in each patient in up to 6 lesions with the highest uptake. We compared the semi-quantitative measurements in the detected lesions grouped by location between 68Ga-RM2 and 68Ga-PSMA11. Results: Four patients had negative 68Ga-RM2 and 68Ga-PSMA11. 68Ga-RM2 PET/MRI identified 50 lesions (average SUVmax 11.40) in 21 patients with a mean PSA value of 8.41. Eight patients had negative 68Ga-RM2 PET/MRI; their average PSA value was 2.89. 68Ga-PSMA11 PET/CT identified 56 lesions (average SUVmax 13.49) in 23 patients with a mean PSA value of 7.97. Six patients had a negative 68Ga-PSMA11 PET/CT; their average PSA value was 2.72. A total of 48 lesions in 19 patients were detected by both 68Ga-RM2 and 68Ga-PSMA11. SUVmax ranged 2.46 - 77.07 (mean±SD:11.95±13.93) and 1.61 - 58.38 (mean±SD:13.80±12.37) for 68Ga-RM2 and 68Ga-PSMA11, respectively. 68Ga-RM2 PET/MRI detected 3 more lesions in 2 patients compared to 68Ga-PSMA11 PET/CT (all lymph-nodes); mean PSA value of these patients was 3. 68Ga-PSMA11 PET/CT detected 10 more lesions in 7 patients compared to 68Ga-RM2 (8 lymph-nodes, 1 lung nodule, 1 bone metastasis); mean PSA values of these patients was 3.69. The semi-quantitative measurements comparison is shown in Table 1. CONCUSIONS: 68Ga-RM2 and 68Ga-PSMA11 are useful radiotracers in the evaluation of BCR PC, with different localization of lesions but similar semi-quantitative measurements. In the age of personalized medicine and theragnostics, it is important to identify which patient will benefit from one class of radiopharmaceutical vs the other. Further evaluation in larger cohorts are needed to confirm our data.