The low-energy β− and electron emitter 161Tb as an alternative to 177Lu for targeted radionuclide therapy

Abstract Introduction The low-energy β − emitter 161 Tb is very similar to 177 Lu with respect to half-life, beta energy and chemical properties. However, 161 Tb also emits a significant amount of conversion and Auger electrons. Greater therapeutic effect can therefore be expected in comparison to 177 Lu. It also emits low-energy photons that are useful for gamma camera imaging. Methods The 160 Gd(n,γ) 161 Gd→ 161 Tb production route was used to produce 161 Tb by neutron irradiation of massive 160 Gd targets (up to 40 mg) in nuclear reactors. A semiautomated procedure based on cation exchange chromatography was developed and applied to isolate no carrier added (n.c.a.) 161 Tb from the bulk of the 160 Gd target and from its stable decay product 161 Dy. 161 Tb was used for radiolabeling DOTA-Tyr3-octreotate; the radiolabeling profile was compared to the commercially available n.c.a. 177 Lu. A 161 Tb Derenzo phantom was imaged using a small-animal single-photon emission computed tomography camera. Results Up to 15 GBq of 161 Tb was produced by long-term irradiation of Gd targets. Using a cation exchange resin, we obtained 80%–90% of the available 161 Tb with high specific activity, radionuclide and chemical purity and in quantities sufficient for therapeutic applications. The 161 Tb obtained was of the quality required to prepare 161 Tb–DOTA-Tyr3-octreotate. Conclusions We were able to produce 161 Tb in n.c.a. form by irradiating highly enriched 160 Gd targets; it can be obtained in the quantity and quality required for the preparation of 161 Tb-labeled therapeutic agents.