Cyclotron production of ⁴³Sc for PET imaging

Abstract

Background

Recently, significant interest in ⁴⁴Sc as a tracer for positron emission tomography (PET) imaging has been observed. Unfortunately, the co-emission by ⁴⁴Sc of high-energy γ rays ( E _γ = 1157, 1499 keV) causes a dangerous increase of the radiation dose to the patients and clinical staff. However, it is possible to produce another radionuclide of scandium— ⁴³Sc—having properties similar to ⁴⁴Sc but is characterized by much lower energy of the concurrent gamma emissions. This work presents the production route of ⁴³Sc by α irradiation of natural calcium, its separation and purification processes, and the labeling of [DOTA,Tyr3] octreotate (DOTATATE) bioconjugate.

Methods

Natural CaCO ₃ and enriched [ ⁴⁰Ca]CaCO ₃ were irradiated with alpha particles for 1 h in an energy range of 14.8–30 MeV at a beam current of 0.5 or 0.25 μA. In order to find the optimum method for the separation of ⁴³Sc from irradiated calcium targets, three processes previously developed for ⁴⁴Sc were tested. Radiolabeling experiments were performed with DOTATATE radiobioconjugate, and the stability of the obtained ⁴³Sc-DOTATATE was tested in human serum.

Results

Studies of ^natCaCO ₃ target irradiation by alpha particles show that the optimum alpha particle energies are in the range of 24–27 MeV, giving 102 MBq/μA/h of ⁴³Sc radioactivity which creates the opportunity to produce several GBq of ⁴³Sc. The separation experiments performed indicate that, as with ⁴⁴Sc, due to the simplicity of the operations and because of the chemical purity of the ⁴³Sc obtained, the best separation process is when UTEVA resin is used. The DOTATATE conjugate was labeled by the obtained ⁴³Sc with a yield >98 % at elevated temperature.

Conclusions

Tens of GBq activities of ⁴³Sc of high radionuclidic purity can be obtainable for clinical applications by irradiation of natural calcium with an alpha beam.