Speaker
Description
Studies in the efficacy of 161Tb production through the neutron activation of 160Gd are especially important, as 161Tb is a well-known alternative to 177Lu, and is often considered superior [1] in battling CRPC (castration-resistant prostate cancer). However, there are many difficulties associated with the procurement of an enriched 160Gd2O3 target, thus necessitating a study regarding the feasibility of 161Tb production through the neutron capture process on natural gadolinium. Natural gadolinium neutron activation poses a significant challenge; there are seven stable isotopes of gadolinium, two of which (155Gd and 157Gd) have exceptionally high cross sections in the thermal neutron region. A way to bypass this problem is explored in this study, by activating natural gadolinium with fast instead of slow neutrons.
The experiment took place at the Extreme Light Infrastructure (ELI-ALPS) Research Institute in Szeged, Hungary. These facilities have the capability of accelerating deuterons with lasers, hitting a deuterated plastic target and therefore producing fast neutrons through the D-D reaction. A sample of metallic natural gadolinium (diameter ~5 mm) was irradiated using neutrons of average energy of approximately 3.05 MeV. Since 161Tb decays through β- emission, producing only low energy gamma rays, the highest of which is 74.6 keV with 10.2% intensity, it was of the outmost importance that the irradiated sample be placed in front of a HPGe detector with a very thin window, inside lead shielding which guarantees a low radiation background. The γ-spectra were acquired and analyzed, the peaks identified and the counts of the relevant photopeaks determined. Theoretical calculations were performed in conjunction with simulations utilizing MCNP to estimate the activity of the natural gadolinium sample. The findings indicate that the production of 161Tb is feasible though in small quantities.
References
[1] Müller, C., Umbricht, C.A., Gracheva, N. et al. Terbium-161 for PSMA-targeted radionuclide therapy of prostate cancer. Eur J Nucl Med Mol Imaging 46, 1919–1930 (2019). https://doi.org/10.1007/s00259-019-04345-0