Chemical properties
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 .
Nuclear properties
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.
Moreover Tb-161 emits gamma- 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].
Production
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®) .
Distribution
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
Parameter | Specification |
---|---|
Half-life | 6.95 d |
Daughter | Dy-161 (stable) |
Branching Ratio/Decay | 100% β- |
Production | Gd-160(n,γ)Gd-161(β-)Tb-161 |
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 |
Chemical Purity | t.b.d. |
Identification | 48.9 keV and 74.6 keV lines present |
Appearance | Clear and colourless solution |
pH | 1-2 |
Activity available | ~GBq (depends on PRISMAP lab) |
Availability | Monthly (planning in advance) |
Grade | Preclinical grade, n.c.a. |
Other information | with/without analysis certificate |