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.
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
|Branching Ratio/Decay||100% EC|
|Production||Ta(p,spallation) or Gd(p,X)|
|Purification||Off-line mass separation + 2-step column separation|
|Chemical Form||In 0.05 M HCl|
|Chemical Purity||n.a. (analytical grade chemicals, datasheet upon request)|
|Identification||Presence of 86.6 keV, 105.3 keV and 180.1 keV gamma lines|
|Activity available||TBD (under commissioning)|
|Availability||Few times per year (planning in advance)|
|Other information||Research grade implanted (with >10% Ce-139) in Al, Zn or NaCl layer on Au foil also possible|