Production and characterization of no-carrier-added (161)Tb as an alternative to the clinically-applied (177)Lu for radionuclide therapy

BACKGROUND: (161)Tb is an interesting radionuclide for cancer treatment, showing similar decay characteristics and chemical behavior to clinically-employed (177)Lu. The therapeutic effect of (161)Tb, however, may be enhanced due to the co-emission of a larger number of conversion and Auger electrons as compared to (177)Lu. The aim of this study was to produce (161)Tb from enriched (160)Gd targets in quantity and quality sufficient for first application in patients. METHODS: No-carrier-added (161)Tb was produced by neutron irradiation of enriched (160)Gd targets at nuclear research reactors. The (161)Tb purification method was developed with the use of cation exchange (Sykam resin) and extraction chromatography (LN3 resin), respectively. The resultant product ((161)TbCl(3)) was characterized and the (161)Tb purity compared with commercial (177)LuCl(3). The purity of the final product ((161)TbCl(3)) was analyzed by means of γ-ray spectrometry (radionuclidic purity) and radio TLC (radiochemical purity). The radiolabeling yield of (161)Tb-DOTA was assessed over a two-week period post processing in order to observe the quality change of the obtained (161)Tb towards future clinical application. To understand how the possible drug products (peptides radiolabeled with (161)Tb) vary with time, stability of the clinically-applied somatostatin analogue DOTATOC, radiolabeled with (161)Tb, was investigated over a 24-h period. The radiolytic stability experiments were compared to those performed with (177)Lu-DOTATOC in order to investigate the possible influence of conversion and Auger electrons of (161)Tb on peptide disintegration. RESULTS: Irradiations of enriched (160)Gd targets yielded 6–20 GBq (161)Tb. The final product was obtained at an activity concentration of 11–21 MBq/μL with ≥99% radionuclidic and radiochemical purity. The DOTA chelator was radiolabeled with (161)Tb or (177)Lu at the molar activity deemed useful for clinical application, even at the two-week time point after end of chemical separation. DOTATOC, radiolabeled with either (161)Tb or (177)Lu, was stable over 24 h in the presence of a stabilizer. CONCLUSIONS: In this study, it was shown that (161)Tb can be produced in high activities using different irradiation facilities. The developed method for (161)Tb separation from the target material yielded (161)TbCl(3) in quality suitable for high-specific radiolabeling, relevant for future clinical application. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s41181-019-0063-6) contains supplementary material, which is available to authorized users.