Tb-155 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-155 too, in particular DOTA, but also others. Also radiolabelling of heat-sensitive molecules with Tb radionuclides has been reported .
Tb-155 decays by electron-capture with a half-life of 5.32(6) days to stable Gd-155. Its half-life of several days is close to the physical half-life of the therapeutic Tb-161 radiolanthanide and of Lu-177, therefore allowing for extended imaging studies.
Tb-155 emits low energy conversion and Auger electrons with an average of 2.0 electrons (with energies above 4 keV) per decay.
Tb-155 emits γ- and X-rays, notably 107(1) % around 45(+/-11%) keV, and 32.0(18) % at 86.6 keV and 25.1% at 105.3 keV . These make Tb-155 suitable for SPECT-imaging.
The mean electron energy emitted per decay is 38 keV, the mean photon energy per decay is 175 keV.
Tb-155 is produced by high energy proton induced spallation of tantalum targets at the production facility MEDICIS at CERN. An off-line mass separation is performed at MEDICIS at CERN. The mass-separated ions are implanted into a solid matrix, e.g. an Al, Zn or NaCl layer on a noble metal backing. The implanted layer is then dissolved and used for an additional radiochemical separation to obtain optimum radionuclidic purity by removing the pseudo-isobar Ce-139 that is mass-separated as oxide ions on mass 155.
Radiochemical separations are performed at the PRISMAP production facilities PSI SINQ and Injector 2 (PSI, Villigen, Switzerland), BR2 (SCK CEN, Mol, Belgium) or MARIA (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.
Radiochemical separations is performed directly at MEDICIS at CERN, Switzerland. Activity will be shipped from there in form of TbCl3 solution, ready for labelling of e.g. DOTA-compounds.
Examples of use
|Production route||Ta(p,spallation) or Gd(p,X)|
|Daughter||Decays to stable Gd-155: 100% EC|
|Processing||Off-line mass separation + 2-step column separation|
|Chemical Form||Implanted in solid layer|
|Radioactive Concentration (gamma spectrometry)||n.a.|
|Radionuclide identification (gamma spectrometry)||87 keV, 105 keV and 180 keV gamma lines present|
|Radionuclidic Purity (gamma spectrometry)||t.b.d.|
|Chemical purity (ICP-OES)||n.a.|
|Molar activity (ICP-OES)||n.a.|
|Apparent Molar Activity||n.a.|
|pH (pH strips)||n.a.|
|Activity available||t.b.d. (under commissioning) few times per year|
|Activity limit for UN2910 (excepted package) shipment||20 MBq in dry state or 2 MBq in liquid form|
|Other information||Research grade implanted (with >10% Ce-139) in Al, Zn or NaCl layer on Au foil also possible|