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

Abstract 

Introduction

The low-energy β⁻ emitter ¹⁶¹Tb is very similar to ¹⁷⁷Lu with respect to half-life, beta energy and chemical properties. However, ¹⁶¹Tb also emits a significant amount of conversion and Auger electrons. Greater therapeutic effect can therefore be expected in comparison to ¹⁷⁷Lu. It also emits low-energy photons that are useful for gamma camera imaging.

Methods

The ¹⁶⁰Gd(n,γ)¹⁶¹Gd→¹⁶¹Tb production route was used to produce ¹⁶¹Tb by neutron irradiation of massive ¹⁶⁰Gd 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.) ¹⁶¹Tb from the bulk of the ¹⁶⁰Gd target and from its stable decay product ¹⁶¹Dy. ¹⁶¹Tb was used for radiolabeling DOTA-Tyr3-octreotate; the radiolabeling profile was compared to the commercially available n.c.a. ¹⁷⁷Lu. A ¹⁶¹Tb Derenzo phantom was imaged using a small-animal single-photon emission computed tomography camera.

Results

Up to 15 GBq of ¹⁶¹Tb was produced by long-term irradiation of Gd targets. Using a cation exchange resin, we obtained 80%–90% of the available ¹⁶¹Tb with high specific activity, radionuclide and chemical purity and in quantities sufficient for therapeutic applications. The ¹⁶¹Tb obtained was of the quality required to prepare ¹⁶¹Tb–DOTA-Tyr3-octreotate.

Conclusions

We were able to produce ¹⁶¹Tb in n.c.a. form by irradiating highly enriched ¹⁶⁰Gd targets; it can be obtained in the quantity and quality required for the preparation of ¹⁶¹Tb-labeled therapeutic agents.

Keywords: Radionuclide therapy, Radiolanthanides, Specific activity, DOTA-peptides