[Zr]Zr-PSMA-617 PET/CT in biochemical recurrence of prostate cancer: first clinical experience from a pilot study including biodistribution and dose estimates.

PURPOSE

Prostate-specific membrane antigen (PSMA)-targeted PET/CT has become increasingly important in the management of prostate cancer, especially in localization of biochemical recurrence (BCR). PSMA-targeted PET/CT imaging with long-lived radionuclides as Zr (T = 78.4 h) may improve diagnostics by allowing data acquisition on later time points. In this study, we present our first clinical experience including preliminary biodistribution and dosimetry data of [Zr]Zr-PSMA-617 PET/CT in patients with BCR of prostate cancer.

METHODS

Seven patients with BCR of prostate cancer who revealed no (n = 4) or undetermined (n = 3) findings on [Ga]Ga-PSMA-11 PET/CT imaging were referred to [Zr]Zr-PSMA-617 PET/CT. PET/CT imaging was performed 1 h, 24 h, 48 h, and 72 h post injection (p.i.) of 111 ± 11 MBq [Zr]Zr-PSMA-617 (mean ± standard deviation). Normal organ distribution and dosimetry were determined. Lesions visually considered as suggestive of prostate cancer were quantitatively analyzed.

RESULTS

Intense physiological uptake was observed in the salivary and lacrimal glands, liver, spleen, kidneys, intestine and urinary tract. The parotid gland received the highest absorbed dose (0.601 ± 0.185 mGy/MBq), followed by the kidneys (0.517 ± 0.125 mGy/MBq). The estimated overall effective dose for the administration of 111 MBq was 10.1 mSv (0.0913 ± 0.0118 mSv/MBq). In 6 patients, and in particular in 3 of 4 patients with negative [Ga]Ga-PSMA-11 PET/CT, at least one prostate cancer lesion was detected in [Zr]Zr-PSMA-617 PET/CT imaging at later time points. The majority of tumor lesions were first visible at 24 h p.i. with continuously increasing tumor-to-background ratio over time. All tumor lesions were detectable at 48 h and 72 h p.i.

CONCLUSION

[Zr]Zr-PSMA-617 PET/CT imaging is a promising new diagnostic tool with acceptable radiation exposure for patients with prostate cancer especially when [Ga]Ga-PSMA-11 PET/CT imaging fails detecting recurrent disease. The long half-life of Zr enables late time point imaging (up to 72 h in our study) with increased tracer uptake in tumor lesions and higher tumor-to-background ratios allowing identification of lesions non-visible on [Ga]Ga-PSMA-11 PET/CT imaging.