67 Ga-PSMA I&T for Radioguided Surgery of Lymph Node Metastases in Patients With Biochemical Recurrence of Prostate Cancer

Purpose: Radioguided lymph node dissection in patients with prostate cancer, and suffering from biochemical recurrence has been described thoroughly during the past few years. Several prostate-specific membrane antigen (PSMA)-directed ligands labeled with 111 In, 99m Tc, and 68 Ga have been published; however, limitations regarding availability, short half-life, high costs, and unfavorable high energy might restrict frequent use. This study aims at introducing 67 Ga as a promising radionuclide for radioguided surgery.

Methods: Retrospective analysis was performed on 6 patients with 7 PSMA-positive lymph node metastases. 67 Ga-PSMA I&T (imaging and therapy) was synthesized in-house and intravenously applied according to §13 2b of the German Medicinal Products Act. Radioguided surgery was performed 24 hours after injection of 67 Ga-PSMA I&T using a gamma probe. Patient urine samples were collected. Occupational and waste dosimetry was performed to describe hazards arising from radiation.

Results: 67 Ga-PSMA application was tolerated without adverse effects. Five of 7 lymph nodes were detected on 22-hour SPECT/CT in 4 of 6 patients. During surgery, all 7 lymph node metastases were identified by positive gamma probe signal. Relevant accumulation of 67 Ga was observed in lymph node metastases (32.1 ± 15.1 kBq). Histology analysis of near-field lymph node dissection revealed more lymph node metastases than PET/CT (and gamma probe measurements) identified. Waste produced during inpatient stay required decay time of up to 11 days before reaching exemption limits according to German regulations.

Conclusions: Radioguided surgery using 67 Ga-PSMA I&T is a safe and feasible option for patients suffering from biochemical recurrence of prostate cancer. 67 Ga-PSMA I&T was successfully synthesized according to Good Manufacturing Practice guidelines. Radioguided surgery with 67 Ga-PSMA I&T does not lead to relevant radiation burden to urology surgeons and represents a novel interdisciplinary approach in nuclear medicine and urology.