Outstanding increase in tumor-to-background ratio over time allows tumor localization by [ 89 Zr]Zr-PSMA-617 PET/CT in early biochemical recurrence of prostate cancer

Positron emission tomography/computed tomography (PET/CT) using prostate-specific membrane antigen (PSMA)-targeted radiotracers labeled with zirconium-89 ( Zr; half-life ~ 78.41 h) showed promise in localizing biochemical recurrence of prostate cancer (BCR) in pilot studies. Retrospective analysis of 38 consecutive men with BCR (median [minimum-maximum] prostate-specific antigen 0.52 (0.12-2.50 ng/mL) undergoing [ Zr]Zr-PSMA-617 PET/CT post-negative [ Ga]Ga-PSMA-11 PET/CT. PET/CT acquisition 1-h, 24-h, and 48-h post-injection of a median (minimum-maximum) [ Zr]Zr-PSMA-617 tracer activity of 123 (84-166) MBq. [ Zr]Zr-PSMA-617 PET/CT detected altogether 57 lesions: 18 local recurrences, 33 lymph node metastases, 6 bone metastases in 30/38 men with BCR (78%) and prior negative conventional PSMA PET/CT. Lesion uptake significantly increased from 1-h to 24-h and, in a majority of cases, from 24-h to 48-h. Tumor-to-background ratios significantly increased over time, with absolute increases of 100 or more. No side effects were noted. After [ Zr]Zr-PSMA-617 PET/CT-based treatment, prostate-specific antigen concentration decreased in all patients, becoming undetectable in a third of patients. retrospective, single center design; infrequent histopathological and imaging verification. This large series provides further evidence that [ Zr]Zr-PSMA-617 PET/CT is a beneficial imaging modality to localize early BCR. A remarkable increase in tumor-to-background ratio over time allows localization of tumor unidentified on conventional PSMA PET/CT.