# Terbium-161

Source: https://nuclide.cc/isotopes/tb-161/  
Nuclide record `tb-161` (Isotope). Data CC BY-NC 4.0, attribute "Data from Nuclide (nuclide.cc)"; commercial use needs a licence.

## TL;DR

A radioactive metal, chemically almost identical to the widely-used lutetium-177, that gives off the same kind of medium-range particles plus a burst of extra very-short-range electrons. Those extra electrons may let it do more damage to a cancer cell than lutetium-177 while using the same delivery molecules.

## Summary

Terbium-161 decays by beta-minus emission with a half-life of 6.95 days (very close to lutetium-177's 6.65 days) to stable dysprosium-161, and shares much of 177Lu's chemistry (both are trivalent lanthanides suited to DOTA-type chelators), so it can be substituted directly into existing DOTATATE, DOTATOC and PSMA-617-type ligands.

What distinguishes it is a large yield of low-energy conversion and Auger electrons -- roughly 2.3 electrons above 3 keV per decay, with ranges from nanometres to a few tens of nanometres -- alongside its 154 keV mean-energy beta particles, which give it a mean tissue range similar to 177Lu (about 0.7 mm) but potentially more damage to single cells and micrometastases through the additional short-range electrons. It also emits imageable gamma/X-rays around 48.9 keV (17%) and 74.6 keV (10%), suitable for SPECT, including simultaneous dual-isotope imaging alongside 177Lu.

Production is analogous to no-carrier-added 177Lu: thermal-neutron irradiation of enriched gadolinium-160 targets produces short-lived 161Gd (half-life 3.66 minutes), which beta-decays to 161Tb; the Tb is then chemically separated from the bulk Gd. It therefore depends on the same high-flux research reactors used for 177Lu (a European PRISMAP network of ILL, SCK CEN and NCBJ reactors, plus PSI's SINQ spallation source, and a University of Utah TRIGA/University of Missouri collaboration in the US), and remains available only in gigabecquerel, research-scale monthly batches. Terbium-161-labelled PSMA and somatostatin-receptor agents are in early clinical investigation and are not approved by the FDA or EMA.

## Fields

- Kind: Isotope
- Status: phase-1
- Last checked: 2026-09-22
- Also known as: 161Tb; Tb-161
- Tags: therapy; beta emitter; auger electron emitter; research-only

## Sources

- Opportunities and potential challenges of using terbium-161 (Eur J Nucl Med Mol Imaging, 2023): https://link.springer.com/article/10.1007/s00259-023-06316-y
- Potentials and practical challenges of terbium-161 labeled radiopharmaceuticals (PMC, 2025): https://pmc.ncbi.nlm.nih.gov/articles/PMC12494511/
- DOE/isotopes.gov: To Advance Cancer Therapy, University Starts Producing Tb-161: https://www.isotopes.gov/node/1517
- PRISMAP: 161Tb radionuclide portfolio page: https://www.prismap.eu/radionuclides/portfolio/161Tb/

## Connected records

- isotopes: [Lutetium-177](https://nuclide.cc/isotopes/lu-177/)
- technologies: [Auger-electron therapy](https://nuclide.cc/technologies/auger-electron-therapy/), [Peptide receptor radionuclide therapy (PRRT)](https://nuclide.cc/technologies/prrt/)
- ideas: [Fund alpha emitters beyond actinium-225: lead-212, terbium-149 and astatine-211](https://nuclide.cc/ideas/idea-reg-alpha-emitter-portfolio/), [Terbium-161 instead of lutetium-177 in the same ligands](https://nuclide.cc/ideas/idea-tb161-instead-of-lu177/)
- companies: [China Isotope & Radiation Corporation](https://nuclide.cc/companies/china-isotope-radiation/), [Radiopharm Theranostics](https://nuclide.cc/companies/radiopharm-theranostics/)
- trials: [A Study of Terbium 161 (161Tb)-RAD402 in Participants With CRPC](https://nuclide.cc/trials/nct07259213/)
- targets: [5T4 (trophoblast glycoprotein)](https://nuclide.cc/targets/tpbg-5t4/)

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