{"entity":{"id":"tb-161","kind":"isotope","name":"Terbium-161","aka":["161Tb","Tb-161"],"tldr":"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.\n\nWhat 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.\n\nProduction 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.","status":"phase-1","asOf":"2026-09-22","links":[{"label":"Opportunities and potential challenges of using terbium-161 (Eur J Nucl Med Mol Imaging, 2023)","url":"https://link.springer.com/article/10.1007/s00259-023-06316-y"},{"label":"Potentials and practical challenges of terbium-161 labeled radiopharmaceuticals (PMC, 2025)","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC12494511/"},{"label":"DOE/isotopes.gov: To Advance Cancer Therapy, University Starts Producing Tb-161","url":"https://www.isotopes.gov/node/1517"},{"label":"PRISMAP: 161Tb radionuclide portfolio page","url":"https://www.prismap.eu/radionuclides/portfolio/161Tb/"}],"tags":["therapy","beta emitter","auger electron emitter","research-only"],"related":["lu-177","prrt","idea-reg-alpha-emitter-portfolio","auger-electron-therapy"],"indications":[],"sections":[],"technologies":[],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":[],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"symbol":"161Tb","element":"Terbium","massNumber":161,"halfLife":"6.95 days","emissions":["β− mean 154 keV (to stable 161Dy)","conversion + Auger electrons (~2.27 per decay, >3 keV)","γ/X-ray 48.9 keV (17%)","γ/X-ray 74.6 keV (10.2%)"],"emissionClass":"mixed","use":"therapy","tissueRange":"Mean about 0.7 mm (beta), plus nanometre-to-tens-of-nanometre range from Auger/conversion electrons","production":"Reactor: thermal-neutron irradiation of enriched gadolinium-160, 160Gd(n,γ)161Gd, which beta-decays (t1/2 3.66 min) to 161Tb; chemically separated from the Gd target.","supply":"research-only","supplyNote":"Produced at gigabecquerel, monthly-batch scale by the European PRISMAP network (ILL, SCK CEN, NCBJ reactors; PSI's SINQ) and by a University of Utah/University of Missouri TRIGA-reactor collaboration; not yet available at Lu-177-scale clinical supply.","chelators":["DOTA","DOTATATE/DOTATOC-type macrocycles"],"pairedWith":["ga-68"]},"route":"/isotopes/tb-161/","neighbours":{"isotope":[{"id":"lu-177","kind":"isotope","name":"Lutetium-177","route":"/isotopes/lu-177/"}],"technology":[{"id":"auger-electron-therapy","kind":"technology","name":"Auger-electron therapy","route":"/technologies/auger-electron-therapy/"},{"id":"prrt","kind":"technology","name":"Peptide receptor radionuclide therapy (PRRT)","route":"/technologies/prrt/"}],"idea":[{"id":"idea-reg-alpha-emitter-portfolio","kind":"idea","name":"Fund alpha emitters beyond actinium-225: lead-212, terbium-149 and astatine-211","route":"/ideas/idea-reg-alpha-emitter-portfolio/"},{"id":"idea-tb161-instead-of-lu177","kind":"idea","name":"Terbium-161 instead of lutetium-177 in the same ligands","route":"/ideas/idea-tb161-instead-of-lu177/"}],"company":[{"id":"china-isotope-radiation","kind":"company","name":"China Isotope & Radiation Corporation","route":"/companies/china-isotope-radiation/"},{"id":"radiopharm-theranostics","kind":"company","name":"Radiopharm Theranostics","route":"/companies/radiopharm-theranostics/"}],"trial":[{"id":"nct07259213","kind":"trial","name":"A Study of Terbium 161 (161Tb)-RAD402 in Participants With CRPC","route":"/trials/nct07259213/"}],"target":[{"id":"tpbg-5t4","kind":"target","name":"5T4 (trophoblast glycoprotein)","route":"/targets/tpbg-5t4/"}]}}