¹⁸F-rhPSMA-7 PET for the Detection of Biochemical Recurrence of Prostate Cancer After Curative-Intent Radiation Therapy: A Bicentric Retrospective Study

This bicentric, retrospective analysis investigated the efficacy of PET/CT with a novel theranostic prostate-specific membrane antigen (PSMA)-targeting ligand,¹⁸F-rhPSMA-7, in patients with biochemical recurrence (BCR) of prostate cancer after curative-intent primary radiotherapy. Methods: Datasets from patients with BCR of prostate cancer after external-beam radiation therapy or brachytherapy who underwent¹⁸F-rhPSMA-7 PET/CT at eitherTechnical University Munich orLudwig-Maximilians-University Munich were retrospectively reviewed by experienced nuclear medicine physicians and radiologists at both centers. The median injected activity was 299 MBq (range, 204-420 MBq), and the median uptake time was 77 min (range, 46-120 min). All lesions suggestive of recurrent prostate cancer were noted. Detection rates were correlated with patients' prostate-specific antigen (PSA) level, primary Gleason score, and prior use of androgen-deprivation therapy (ADT). Results: Ninety-seven patients were included (65 at Technical University Munich and 32 at Ludwig-Maximilians-University Munich). The median prescan PSAwas 4.19 ng/mL (range, 0.1-159 ng/mL). The primary Gleason score was #6in19patients,7in25,$8in33,and unknownin20.ThirtypatientsreceivedADTinthe6moprecedingPET/ CT.¹⁸F-rhPSMA-7 identified lesions in 91 of 97 (94%) patients. Detection rates stratified by PSA were 88% (22/25), 97% (30/31), 90% (19/ 21),and 100%(20/20)foraPSAof,2,2-,5,5-,10,and$10ng/mL, respectively. Detection rates in the subgroup of patients not meeting the Phoenix criteria for BCR were 80% (4/5), 90% (9/10), 100% (4/4), and 83% (5/6) for a PSA of, 0.5, 0.5-,1, 1-,1.5, and 1.5-2ng/mL, respectively. There were no significant differences in detection rates between patients with and without prior ADT (100% vs. 91%, P 5 0.173) or patients with a Gleason score of #7 and a Gleason score of $8 (98% vs. 91%, P 5 0.316).¹⁸F-rhPSMA-7 revealed local recurrence in 80% (78/97); pelvic lymph node metastases in 38% (37/97); retroperitoneal and supradiaphragmatic lymph node metastases in 9% (9/97) and 4% (4/97), respectively; bone metastases in 27% (26/97); and visceral metastases in 3% (3/97). In the subgroup of patients with a PSAof,2 ng/mL above nadir, local recurrence occurred in 76% (19/ 25) and pelvic lymph node metastases in 36% (9/25). Conclusion:¹⁸F-rhPSMA-7 PET/CT demonstrates high detection rates in prostate cancer patients with BCRafterprimaryradiationtherapy, evenatlow PSA values. Its diagnostic efficacy is comparable to published data for other PSMAligands.