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 β- 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 β- 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.
Moreover Tb-161 emits γ- and X-rays, notably 43.1(5) % around 48(+/-10%) keV and 10.3(2) % at 74.6 keV . Both energies make Tb-161 suitable for SPECT imaging.
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 β-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 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
|Daughter||Decays to stable Dy-161: 100% β-|
|Processing||2-step column separation|
|Primary Container||2.5 mL borosilicate glass V-vial with silicon rubber screw cap|
|Physical Form||Liquid or solid deposit|
|Chemical Form||In 0.05 M HCl (evaporation to dryness is also possible)|
|Radioactive Concentration (gamma spectrometry)|
|Appearance||Clear colourless solution|
|Radionuclide identification (gamma spectrometry)||49 keV and 75 keV gamma lines present|
|Radionuclidic Purity (gamma spectrometry)||>99.99% (<0.01% Tb-160)|
|Chemical purity (ICP-OES)||t.b.d.|
|Molar activity (ICP-OES)||>500 GBq/µmol|
|Apparent Molar Activity||Labelling up to 100 MBq/nmol DOTANOC, DOTATATE or p-SCN-Bn-DOTA|
|pH (pH strips)||n.a.|
|Activity available||~GBq (depends on PRISMAP lab) monthly (planning in advance)|
|Activity limit for UN2910 (excepted package) shipment||0.7 GBq in dry state or 70 MBq in liquid form|