Tb-161 is a radiolanthanide, most often in trivalent state and chemically very similar to lutetium. The ionic radius of Tb3+ is 92 pm, i.e. just 7% larger than Lu3+, which explains that macrocyclic chelators suitable for Lu-177 can be directly employed for Tb-161 too, in particular DOTA, but also others . Also Tb-161 radiolabelling of heat-sensitive molecules has been reported .
Tb-161 decays by beta-minus emission with a half-life of 6.953(2) days to stable Dy-161. Its half-life is marginally (<5%) larger than that of Lu-177. In addition to beta-minus emission it shows ample emission of low energy conversion and Auger electrons , thus emitting in total about 2.27 electrons (with energies above 3 keV) per decay.
The mean electron energy emitted per decay is 197 keV, the mean photon energy per decay is 35 keV or 37 keV considering the newly measured photon intensities [, complemented by Evaluated Nuclear Structure Data File (ENSDF) for photons below 45 keV].
Tb-161 is produced indirectly by thermal neutron irradiation of enriched Gd-160 oxide targets in the research reactors of the PRISMAP network: RHF at ILL, BR2 at SCK CEN and MARIA at NCBJ, or the SINQ spallation neutron source at PSI. The short-lived Gd-161 produced upon neutron capture of Gd-160 decays quickly (T1/2=3.66 min) to Tb-161 via beta-minus decay. A radiochemical Tb/Gd separation via cation exchange and extraction chromatography leads to n.c.a. Tb-161 . The effective specific activity of such produced n.c.a. Tb-161 is comparable to that of commercially available n.c.a. Lu-177 (EndolucinBeta®) .
Radiochemical separations are performed at the PRISMAP facilities PSI Radiochemistry Laboratory (PSI, Villigen, Switzerland), SCK CEN (Mol, Belgium) or POLATOM (NCBJ, Otwock-Swierk, Poland). Activity will be shipped from one of these locations to the users in form of TbCl3 solution, ready for labelling of e.g. DOTA-compounds.
Examples of use
|Branching Ratio/Decay||100% β-|
|Purification||2-step column separation|
|Chemical Form||In 0.05 M HCl (evaporation to dryness is also possible)|
|Specific Activity||>20 GBq/mg (PSI), t.b.d. (SCK CEN and NCBJ)|
|Radionuclide Purity||>99.99% (<0.01% Tb-160)|
|Radioisotopic Purity||>99.99% (<0.01% Tb-160)|
|Radiochemical purity||Labelling up to 100 MBq/nmol DOTANOC, DOTATATE or p-SCN-Bn-DOTA|
|Identification||48.9 keV and 74.6 keV lines present|
|Appearance||Clear and colourless solution|
|Activity available||~GBq (depends on PRISMAP lab)|
|Availability||Monthly (planning in advance)|
|Grade||Preclinical grade, n.c.a.|
|Other information||with/without analysis certificate|