212Pb is a promising radionuclide for targeted alpha particle therapy for cancer. Ongoing preclinical and clinical studies are investigating the potential of 212Pb-labeled peptides and antibodies [1,2,3,4,5]. PSC-PEG2-TOC (VMT-α-NET) is a novel somatostatin receptor subtype 2 (SSTR2) targeting peptide for the treatment of neuroendocrine tumors (NET) that shows rapid tumor accumulation, high tumor retention, and fast renal excretion with the potential for low nephrotoxicity [6, 7].

Here, we present the case of a 75-year-old woman with an advanced G2 NET of unknown primary with liver metastases who was heavily pretreated with somatostatin analogs, various chemotherapies, multiple cycles of [177Lu]Lu-DOTA-TATE and [225Ac]Ac-DOTA-TATE, and radioembolization over 7 years. The patient received 90 MBq of [212Pb]Pb-VMT-α-NET intravenously. Whole-body scintigraphy and SPECT/CT acquisitions were performed 2, 5, and 19 h after injection on a Symbia Intevo 6 (Siemens Healthineers) using high-energy collimators. Images were obtained by detection of the characteristic X-ray emissions of 212Pb using an energy window at 79 keV (40% width). The whole-body scan speed was 8 cm/min, and SPECT/CT scans were acquired with 120 projections (60 per detector, 30 s per projection) over a non-circular 360° orbit. The SPECT/CT images showed a high accumulation of [212Pb]Pb-VMT-α-NET in liver metastases in segments III and IV, consistent with the previously acquired [68Ga]Ga-DOTA-TATE PET/CT. High tumor retention can be observed in the planar and SPECT/CT images over time. The planar images showed a high level of background noise due to down-scatter and septal penetration of high-energy photon emissions from 212Pb daughter nuclides (e.g., 2.6 MeV from 208Tl). Due to the short half-life of 212Pb (10.6 h), the images acquired after 19 h showed a relatively high level of image noise due to the low count statistics. The patient showed no early or acute adverse events.

These are the first clinical post-treatment scintigraphic images of [212Pb]Pb-VMT-α-NET and additionally the first-in-human SPECT/CT images of 212Pb.

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