PSA-stratified detection rates for [ 68 Ga]THP-PSMA, a novel probe for rapid kit-based 68 Ga-labeling and PET imaging, in patients with biochemical recurrence after primary therapy for prostate cancer

Abstract

Purpose

[⁶⁸Ga]Tris(hydroxypyridinone)(THP)-PSMA is a novel radiopharmaceutical for one-step kit-based radiolabelling, based on direct chelation of ⁶⁸Ga³⁺ at low concentration, room temperature and over a wide pH range, using direct elution from a ⁶⁸Ge/⁶⁸Ga-generator. We evaluated the clinical detection rates of [⁶⁸Ga]THP-PSMA PET/CT in patients with biochemically recurrent prostate cancer after prostatectomy.

Methods

Consecutive patients (n=99) referred for evaluation of biochemical relapse of prostate cancer by [⁶⁸Ga]THP-PSMA PET/CT were analyzed retrospectively. Patients underwent a standard whole-body PET/CT (1 h p.i.), followed by delayed (3 h p.i.) imaging of the abdomen. PSA-stratified cohorts of positive PET/CT results, standardized uptake values (SUVs) and target-to-background ratios (TBRs) were analyzed, and compared between standard and delayed imaging.

Results

At least one lesion suggestive of recurrent or metastatic prostate cancer was identified on PET images in 52 patients (52.5%). Detection rates of [⁶⁸Ga]THP-PSMA PET/CT increased with increasing PSA level: 94.1% for a PSA value of ≥10 ng/mL, 77.3% for a PSA value of 2 to <10 ng/mL, 54.5% for a PSA value of 1 to <2 ng/mL, 14.3% for a PSA value of 0.5 to <1 ng/mL, 20.0% for a PSA value of >0.2 to <0.5, and 22.2% for a PSA value of 0.01 to 0.2 ng/mL. [⁶⁸Ga]THP-PSMA uptake (SUVs) in metastases decreased over time, whereas TBRs improved. Delayed imaging at 3 h p.i. exclusively identified pathologic findings in 2% of [⁶⁸Ga]THP-PSMA PET/CT scans. Detection rate was higher in patients with a Gleason score ≥8 (P=0.02) and in patients receiving androgen deprivation therapy (P=0.003).

Conclusions

In this study, [⁶⁸Ga]THP-PSMA PET/CT showed suitable detection rates in patients with biochemical recurrence of prostate cancer and PSA levels ≥ 2 ng /mL. Detections rates were lower than in previous studies evaluating other PSMA ligands, though prospective direct radiotracer comparison studies are mandatory particularly in patients with low PSA levels to evaluate the relative performance of different PSMA ligands.

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