Zirconium-89-based PSMA PET/CT with delayed imaging for early detection of biochemical recurrence in prostate cancer patients with PSA ≤ 0.2 ng/mL: A feasibility study

PSMA PET/CT using PSMA ligands labeled with the long-lived radionuclide zirconium-89 represents a promising novel imaging approach for prostate cancer. Preliminary evidence indicates that [89Zr]Zr-PSMA PET/CT may enhance the detection of tumor lesions in patients with biochemical recurrence (BCR). This study aims to evaluate the positivity rate and feasibility of [89Zr]Zr-PSMA imaging in patients with very low PSA levels (≤ 0.2 ng/mL). Sixty-five patients with BCR and PSA levels ≤ 0.2 ng/mL undergoing [89Zr]Zr-PSMA PET/CT were analyzed. The mean PSA level at imaging was 0.14 ± 0.04 ng/mL. PET/CT was performed using a mean injected activity of 129.0 ± 19.3 MBq and an uptake time of 48 h. Positivity rates and potential predictors of scan positivity, including PSA level, PSA doubling time, and initial Gleason score, were evaluated. [89Zr]Zr-PSMA PET/CT achieved a high overall positivity rate of 72.3%, with 47 of 65 patients presenting with at least one suspicious lesion. Local recurrence was detected in 25 patients, while lymph node and bone metastases were observed in 29 and 4 patients, respectively. Patients with a Gleason score ≥ 8 exhibited a higher positivity rate than those with lower scores (p = 0.047). In patients with BCR and PSA levels ≤ 0.2 ng/mL, [89Zr]Zr-PSMA PET/CT yielded a 72.3% positivity rate in this single-center cohort of 65 individuals. This notable sensitivity at minimal PSA concentrations may enable early identification of recurrent disease and facilitate individualized targeted therapy.