Scandium-47 as a radionuclide precursor: Feasibility of production in a ⁴⁷Ca/⁴⁷Sc generator-like system

Scandium-47 (⁴⁷Sc), a medium-energy β^- emitter with a half-life of 3.35 days and associated γ emission (159 keV, 68.1 %), is an attractive radionuclide for targeted radionuclide therapy and theranostics. Production of ⁴⁷Sc via neutron irradiation of enriched ⁴⁶Ca targets through the ⁴⁶Ca(n,γ)⁴⁷Ca → ⁴⁷Sc decay pathway offers advantages such as thermal neutron utilisation and minimised contaminant co-production. Efficient separation and repeated recovery of ⁴⁷Sc in a quasi-generator system are crucial for enabling its medical application.

Neutron irradiations of calcium carbonate targets ⁴⁶Ca-enriched (5.2 % and 10.5 %) at the Maria research reactor yielded up to 5.18 GBq ⁴⁷Sc and 5.60 GBq ⁴⁷Ca at the end of bombardment. Separation of ⁴⁷Sc from ⁴⁷Ca was performed using DGA resin with recovery efficiencies of 81-97 % for ⁴⁷Sc and 98-99 % for ⁴⁷Ca in up to five consecutive elutions within 18 days. Radiochemical purity of eluted [⁴⁷Sc]ScCl₃ exceeded 95 % in initial separations. Radiolabelling studies with DOTA-TATE demonstrated effective molar activities up to 20 MBq/nmol and radiochemical purities >98 %. Stability tests confirmed that the [⁴⁷Sc]ScCl₃ eluate remained suitable for radiolabelling for the entire testing period of up to 4 days post-elution. Trace metal analysis showed predominantly low contamination levels, with sporadic impurities attributed to handling conditions.

The ⁴⁷Ca/⁴⁷Sc quasi-generator system based on neutron irradiation of enriched ⁴⁶Ca targets offers a reliable source of high-quality ⁴⁷Sc for radiopharmaceutical applications. Multiple elutions from a single target enable sustained production of ⁴⁷Sc with excellent radionuclidic and radiochemical purity. These results support further development of ⁴⁷Sc as a theranostic radionuclide for larger-scale production. A preliminary specification for ⁴⁷Sc as a radionuclide precursor was proposed following the European Pharmacopoeia guidelines, providing a groundwork for future standardisation.