Chemical properties

Pb-203 serves as an ideal SPECT imaging agent that is chemically identical to therapeutic alpha-emitter Pb-212. In aqueous solutions, Pb-203 exists almost exclusively in oxidation state II (Pb²⁺) and coordinates well with multidentate macrocyclic or acyclic chelators (such as DOTA, TCMC, or lead-specific chelators like PSC) containing nitrogen and oxygen donor atoms REF

Nuclear properties

Pb-203 decays with a half-life of 51.92(3)h by electron capture (100 % ε) to stable Tl-203, followed by the emission of one dominant γ-ray at 279.2 keV (80.94(6)%) and X-rays, notably K_α at ≈72 keV (67.1 %) and K_β at ≈83 keV (16.3(3) %).

These energies make Pb-203 suitable for SPECT imaging with particular interest as theranostics counterpart of the α-emitter Pb-212.

The mean electron energy emitted per decay is 44 keV, the mean photon energy per decay is 314 keV.

Production

Pb-203 is produced via deuteron irradiation of enriched Tl-205 targets at ARRONAX (Nantes, France), followed by a radiochemical Pb/Tl separation via ion exchange chromatography.

Distribution

Irradiation and radiochemical separation are performed at ARRONAX (Nantes, France). Activity will be shipped from there to the users in form of 1 M ammonium acetate solution.

Examples of use

• Pb-203 has been used as radiotracer in toxicology studies to quantify uptake and release of lead compounds
• Different lead-specific chelators have been reported
• DOTA can be used efficiently with Pb-203 REF
• Pb-203 may serve as imaging surrogate in the Pb-203/Pb-212 theranostic pair where the latter acts in turn as Pb-212/Bi-212 in-vivo generator of the alpha-emitter Bi-212