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

Abstract

This bi-centric, retrospective analysis investigates the efficacy of PET/CT with novel theranostic PSMA-targeting ligand, ¹⁸F-rhPSMA-7, in patients with biochemical recurrence (BCR) of prostate cancer following curative-intent primary radiotherapy. Methods: Datasets from patients with BCR of prostate cancer following EBRT or brachytherapy who underwent ¹⁸F-rhPSMA-7 PET/CT at either the Technical University of Munich (TUM) or Ludwig-Maximilians-University Munich (LMU) were retrospectively reviewed by experienced nuclear medicine physicians and radiologists in both centers. Median (range) injected activity was 299 (204-420) MBq and median (range) uptake time was 77 (46-120) minutes. All lesions suspicious for recurrent prostate cancer were noted. Detection rates were correlated with patients’ PSA level, primary Gleason score (GS), and prior use of androgen-deprivation therapy (ADT). Results: 97 patients were included (n = 65 TUM and n = 32 LMU). Median (range) pre-scan PSA was 4.19 (0.1-159) ng/mL. Primary GS was ≤6 in 19, 7 in 25, ≥8 in 33 and unknown in 20 patients. 30 patients received ADT in the 6 months preceding PET/CT. ¹⁸F-rhPSMA-7 identified lesions in 91/97 (94%) patients. Detection rates stratified by PSA were 88% (22/25), 97% (30/31), 90% (19/21) and 100% (20/20) for PSA <2, 2–<5, 5–<10, and ≥10 ng/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 PSA <0.5, 0.5–<1, 1–<1.5, and 1.5–2 ng/mL, respectively. There were no significant differences between detection rates among patients with prior ADT and without (100% vs. 91%; P = 0.173) or patients with GS ≤7 vs. ≥8 (98% vs. 91%, P = 0.316).¹⁸F-rhPSMA-7 revealed local recurrence in 80% (78/97), pelvic lymph node metastases in 38% (37/97), retroperitoneal and supra-diaphragmatic lymph nodes 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 PSA<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 BCR after primary RT, even at low PSA-values. Its diagnostic efficacy is comparable to published data for other PSMA-ligands.