Work

Production of the Auger-electron emitter 161Ho for nuclear medicine using proton beams

Year: 2026

Type: article

Abstract: Auger-electron emitters have steadily acquired considerable attention in the last decade due to their potential to treat micrometastases. However, the limited availability of Auger-electron emitters has restricted investigations of the radiobiological effects induced by Auger cascades. Among the medically relevant Auger-electron-emitting radiolanthanides, 161 Ho stands out as a suitable candidate thanks to its high emission of low-energy electrons. Its low-intensity, low-energy γ rays would enable dosimetry evaluation, while minimizing the deposited dose. This project involved the measurement of proton-induced activation cross sections of holmium radioisotopes, focusing on 160m,161cum,162m Ho, using nat,161,162 Dy targets irradiated with an 18 MeV cyclotron at the Bern medical cyclotron laboratory. Additionally, production yields were measured at the Paul Scherrer Institute using a 72 MeV separated-sector cyclotron, where dysprosium targets were irradiated for the 161 Ho direct production and 165 Ho targets to study the indirect production pathway via 161 Er decay. Comparison with previously published experimental data showed good agreement for the production cross sections of relevant holmium radioisotopes, while those of 160g Ho were reported here for the first time. The nuclear reaction cross sections of 161cum,162 g,162m Ho were determined by inverting a system of linear equations. Theoretical predictions from the TENDL 2023 library generally overestimated the experimental excitation functions by up to 50%. Irradiation runs of production targets validated the cross sections measured. 165 Ho emerged as optimal target material for large-scale production of highly radionuclidically pure 161 Ho. Six-hour irradiation of 165 Ho targets yielded 15 GBq of 161 Er’s end-of-bombardment activity at up to 99.98% of radionuclidic purity using 45 MeV proton beams.

Source: Applied Radiation and Isotopes

DOI: 10.1016/j.apradiso.2026.112622