Production of high purity 47Sc from proton irradiation of natural vanadium targets

Background

Scandium-47 is the therapeutic counterpart to the diagnostic radionuclides, ⁴³Sc and ⁴⁴Sc. Together, these form elementally matched theranostic nuclide pairs, but their incorporation into radiopharmaceuticals requires developing production techniques leading to radioscandium isotopes with high chemical and radionuclidic purity. Previous ⁴⁷Sc production methods involved expensive, enriched titanium targets that require additional procedures for target recovery. This work investigates the irradiation of natural vanadium targets and the development of purification methods for high-purity ⁴⁷Sc. Natural vanadium foils were used in cyclotron target configurations. Targets were irradiated with 24 MeV protons at currents of up to 80 µA. A purification method was developed by determining the K_d values of Sc, Cr, and V using MP-50 resin. The final purification method used MP-50 and CM resin columns to isolate the ⁴⁷Sc from ^natV and co-produced ⁵¹Cr. Inductively Coupled Plasma Mass Spectrometry (ICP-MS), gamma-ray spectroscopy, and a DOTA titration were used to characterize the ⁴⁷Sc product.

Results

Two cyclotron targets were designed, a small-scale target for developing a purification procedure and a high-power target for scaled-up production. The high-power target maximum current was 80 µA of 24 MeV protons. The yield for an 8 h irradiation at 80 µA of 24 MeV protons, was 128.02 ± 11.1 MBq of ⁴⁷Sc at End of Bombardment. The radionuclidic purity of ⁴⁷Sc was 99.5 ± 0.2%. The purification using MP-50 and CM columns resulted in the removal of ^natV target and ⁵¹Cr contaminate in the final ⁴⁷Sc product, with an average recovery of 72 ± 2.1% and a DOTA apparent molar activity of 7733 ± 155 MBq/µmol. ICP-MS results showed that all top-row transition metals were below the limit of detection (< 1 ppb) with the exception of Zn, which was 64.6 ± 10.3 ppb.

Conclusions

A high-power cyclotron target capable of withstanding a proton current of 80 µA was developed. A novel separation method was developed for isolating the ⁴⁷Sc from the vanadium target and the co-produced ⁵¹Cr contaminate. The final product characterization resulted in a chemically and radionuclidically pure ⁴⁷Sc product with high recovery yields.