First-in-Human Application of Terbium-161: A Feasibility Study Using ¹⁶¹Tb-DOTATOC

Abstract

¹⁶¹Tb has similar decay properties as ¹⁷⁷Lu but, additionally, emits a substantial number of conversion and Auger electrons. The aim of this study was to apply ¹⁶¹Tb in a clinical setting and to investigate the feasibility to visualize the physiological and tumor biodistribution of ¹⁶¹Tb-DOTATOC. Methods: ¹⁶¹Tb was shipped from Paul Scherrer Institute, Switzerland, to Zentralklinik Bad Berka, Germany, where it was used for the radiolabeling of DOTATOC. In two separate studies, 596 MBq and 1300 MBq ¹⁶¹Tb-DOTATOC were administered to a 35-year-old male patient with metastatic, well differentiated, non-functional malignant paraganglioma and a 70-year-old male patient with a metastatic, functional neuroendocrine neoplasm of the pancreatic tail, respectively. Whole-body planar γ-scintigraphies were acquired over a period of several days for dosimetry calculations. SPECT/CT images were reconstructed, using a recently-established protocol and visually analyzed. Patients were checked for adverse events after application of ¹⁶¹Tb-DOTATOC. Results: The radiolabeling of DOTATOC with ¹⁶¹Tb was readily achieved with high radiochemical purity suitable for patient application. Planar images and dosimetry provided the expected time-dependent biodistribution of ¹⁶¹Tb-DOTATOC in liver, kidneys, spleen and urinary bladder. SPECT/CT images were of high quality and visualized even small metastases in the liver and bones. Application of ¹⁶¹Tb-DOTATOC was well tolerated and no related adverse events were reported. Conclusion: This study demonstrated the feasibility to image even small metastases after injection of relatively low activities of ¹⁶¹Tb-DOTATOC using γ-scintigraphy and SPECT. Based on this essential first step to translate ¹⁶¹Tb to clinics, further efforts will be directed towards the application of ¹⁶¹Tb for therapeutic purposes.