Cross section measurement of terbium radioisotopes for an optimized Tb production with an 18 MeV medical PET cyclotron.

Tb [t = 5.32 d, E = 87 keV (32%); 105 keV (25%) (IAEA, 2021)] is a novel promising radionuclide for theranostic applications in nuclear medicine. Its physical properties make it suitable for single photon emission computed tomography (SPECT) imaging, while its chemistry allows it to be used as a diagnostic partner for therapeutic radiolanthanides or pseudo-radiolanthanides, such as Lu and Y. Moreover, Tb could be used as a precise diagnostic match for the β-emitter Tb, opening doors for the true theranostics concept. The availability of Tb in quantity and quality suitable for medical applications is an open issue and its production with medical cyclotrons via the Gd(p,n)Tb and Gd(p,2n)Tb nuclear reactions represents a possible but challenging solution. For this purpose, an accurate knowledge of the production cross sections is mandatory. In this paper, we report on the measurement of the production cross sections of Tb and other terbium radionuclides formed by proton irradiation of GdO, GdO and GdO enriched targets, performed at the Bern University Hospital cyclotron laboratory. On the basis of the obtained results, the production yield and purity were calculated to assess the optimal irradiation conditions. The results of several production tests are also presented.