First-in-Humans Application of Tb: A Feasibility Study Using Tb-DOTATOC.

Tb has decay properties similar to those of Lu but, additionally, emits a substantial number of conversion and Auger electrons. The aim of this study was to apply Tb in a clinical setting and to investigate the feasibility of visualizing the physiologic and tumor biodistributions of Tb-DOTATOC. Tb was shipped from Paul Scherrer Institute, Villigen-PSI, Switzerland, to Zentralklinik Bad Berka, Bad Berka, Germany, where it was used for the radiolabeling of DOTATOC. In 2 separate studies, 596 and 1,300 MBq of Tb-DOTATOC were administered to a 35-y-old male patient with a metastatic, well-differentiated, nonfunctional malignant paraganglioma and a 70-y-old male patient with a metastatic, functional neuroendocrine neoplasm of the pancreatic tail, respectively. Whole-body planar γ-scintigraphy images 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 observed for adverse events after the application of Tb-DOTATOC. The radiolabeling of DOTATOC with Tb was readily achieved with a high radiochemical purity suitable for patient application. Planar images and dosimetry provided the expected time-dependent biodistribution of Tb-DOTATOC in the liver, kidneys, spleen, and urinary bladder. SPECT/CT images were of high quality and visualized even small metastases in bones and liver. The application of Tb-DOTATOC was well tolerated, and no related adverse events were reported. This study demonstrated the feasibility of imaging even small metastases after the injection of relatively low activities of Tb-DOTATOC using γ-scintigraphy and SPECT/CT. On the basis of this essential first step in translating Tb to clinics, further efforts will be directed toward the application of Tb for therapeutic purposes.