Radiation stability and performance of TEHDGA resin for theranostic scandium radionuclide purification

Scandium radionuclides are emerging theranostic radionuclides that offer matched diagnostic and therapeutic emissions for targeted applications in nuclear medicine. For their safe and effective clinical use, it is crucial to obtain preparations with very high radiochemical purity, which in turn relies on carefully optimized physical separation and chemical purification strategies. A selective and clinically attractive method for purification is ion-exchange solid-phase extraction; however, its performance and expected resin lifetime under high radiation doses and repeated separation cycles remains insufficiently considered. This study provides a critical evaluation of the radiation stability and separation performance of the N, N,N',N'-tetra(2-ethylhexyl)diglycolamide (TEHDGA) ion-exchange resin.

Monte Carlo simulations in RayXpert^® show that assuming 1 GBq ⁴⁴Sc and 3.7 GBq ⁴⁷Sc initial activities (possible theranostic activities) a total absorbed dose of ~ 1 kGy could be expected for ⁴⁴Sc and ~ 5 kGy for ⁴⁷Sc in one purification experiment. EPR spectra show that after irradiation the TEHDGA resin does not form room temperature stable radicals; however, the resin appears to change its chemical structure upon irradiation with electrons in a nitric acid environment, as indicated by ATR-FTIR measurements. However, these chemical changes can be estimated to have little-to-no effect on the practical application of TEHDGA in scandium ion purification, yielding separation efficiency from contaminants of at least 99% for resin irradiated in 2.5 M HNO₃, whereas irradiation in air yielded a minimum separation efficiency of 96%. No clear changes in selectivity, ion-exchange capacity or recoverability have been observed.

TEHDGA resin can be deemed suitable for theranostic scandium radionuclide purification from metallic contaminants; however, further research is needed to assess the possible transient effects of short-lived radiolysis intermediates during practical scandium radionuclide purification.