¹⁸F-rhPSMA-7 positron emission tomography (PET) for the detection of biochemical recurrence of prostate cancer following curative-intent radiation therapy

Objectives: ¹⁸F-rhPSMA-7 is a new theranostic PSMA-targeting agent which allows fast radiolabeling with ¹⁸F and radiometals. This retrospective analysis investigates the efficacy of ¹⁸F-rhPSMA-7 PET/computed tomography (CT) in patients with biochemical recurrence of prostate cancer following curative-intent primary treatment with external beam radiotherapy (EBRT) or brachytherapy.

Methods: Datasets from patients with non-castrate biochemical recurrence of prostate cancer after treatment with EBRT or brachytherapy who underwent ¹⁸F-rhPSMA-7 PET/CT at either the Technical University Munich or Ludwig-Maximillian University, Munich, were retrospectively reviewed. Images were reviewed by two experienced nuclear medicine physician and all lesions suspicious for recurrent prostate cancer were noted. The detection rates were correlated with patients’ PSA level, primary Gleason score, and prior use of androgen deprivation therapy (ADT).

Results: Images from 78 patients were reviewed (65 from scans conducted at the Technical University Munich and 13 from scans at Ludwig-Maximillian University). Patients’ median pre-scan PSA level was 4.6 ng/mL (range: 0-70.0 ng/mL). Of the 78 patients, 61 had received EBRT as their primary therapy, 13 had received brachytherapy, while 4 had received a combination of EBRT and brachytherapy. Twenty-five of the 78 patients had received ADT within the 6 months preceding the scan. The median injected activity of ¹⁸F-rhPSMA-7 was 321 MBq (range 230-420 MBq) and the median uptake time was 79 min (range: 49-125 min). ¹⁸F-rhPSMA-7 PET/CT identified 73 (94%) patients with positive findings indicative of tumour recurrence. The detection rates were 83% (15/18), 100% (26/26), 89% (17/19) and 100% (15/15) for PSA levels < 2, 2 to < 5, 5 to < 10 and ≥ 10 ng/mL, respectively. ¹⁸F-rhPSMA-7 PET/CT revealed local recurrence in 85% (66) patients. Lymph node metastases were present in the pelvis in 33% (26), in the retroperitoneum in 9% (7) and in a supradiaphragmatic location in 4% (3) patients. Bone and visceral metastases were detected in 27% (21) and 4% (3) patients, respectively. Detection rates were not influenced by the prior use of ADT (100% vs. 90% with no prior ADT, p = 0.2) or Gleason score (97% for Gleason Score &#8804; 7 vs. 91% for Gleason Score ≥ 8, p = 0.6).

Conclusions: ¹⁸F-rhPSMA-7 PET/CT demonstrates high detection rates in patients with biochemical recurrence of prostate cancer after primary radiation therapy. The detection rate was broadly proportional to PSA level and appears to be similar to published data for other PSMA ligands.