Cross-section measurement of thulium radioisotopes with an 18 MeV medical PET cyclotron for an optimized 165Er production

Gaia Dellepiane; Pierluigi Casolaro; Chiara Favaretto; Alexander Gottstein; Pascal V Grundler; Isidre Mateu; Edoardo Renaldin; Paola Scampoli; Zeynep Talip; Nicholas P van der Meulen; Saverio Braccini

doi:10.1016/j.apradiso.2023.110954

Cross-section measurement of thulium radioisotopes with an 18 MeV medical PET cyclotron for an optimized ¹⁶⁵Er production

Appl Radiat Isot. 2023 Oct:200:110954. doi: 10.1016/j.apradiso.2023.110954. Epub 2023 Jul 24.

Affiliations

¹ Albert Einstein Center for Fundamental Physics (AEC), Laboratory for High Energy Physics (LHEP), University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland. Electronic address: gaia.dellepiane@lhep.unibe.ch.
² Albert Einstein Center for Fundamental Physics (AEC), Laboratory for High Energy Physics (LHEP), University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland.
³ Center for Radiopharmaceutical Sciences, ETH-PSI-USZ, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland; Division of Nuclear Medicine, University Hospital Basel, 4031 Basel, Switzerland.
⁴ Center for Radiopharmaceutical Sciences, ETH-PSI-USZ, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
⁵ Albert Einstein Center for Fundamental Physics (AEC), Laboratory for High Energy Physics (LHEP), University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland; Department of Physics "Ettore Pancini", University of Napoli Federico II, Complesso Universitario di Monte S. Angelo, 80126 Napoli, Italy.
⁶ Center for Radiopharmaceutical Sciences, ETH-PSI-USZ, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland; Laboratory of Radiochemistry, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.

PMID: 37527621
DOI: 10.1016/j.apradiso.2023.110954

Abstract

¹⁶⁵Er is a pure Auger-electron emitter with promising characteristics for therapeutic applications in nuclear medicine. The short penetration path and high Linear Energy Transfer (LET) of the emitted Auger electrons make ¹⁶⁵Er particularly suitable for treating small tumor metastases. Several production methods based on the irradiation with charged particles of Er and Ho targets can be found in the literature. In this paper, we report on the study of ¹⁶⁵Er indirect production performed via the ¹⁶⁶Er(p,2n)¹⁶⁵Tm →¹⁶⁵Er reaction at the 18 MeV Bern medical cyclotron. Despite the use of highly enriched ¹⁶⁶Er₂O₃ targets, several Tm radioisotopes are produced during the irradiation, making the knowledge of the cross sections involved crucial. For this reason, a precise investigation of the cross sections of the relevant nuclear reactions in the energy range of interest was performed by irradiating Er₂O₃ targets with different isotopic enrichment levels and using a method based on the inversion of a linear system of equations. For the reactions ¹⁶⁴Er(p, γ)¹⁶⁵Tm, ¹⁶⁶Er(p,n)¹⁶⁶Tm, ¹⁶⁶Er(p, γ)¹⁶⁷Tm, ¹⁶⁷Er(p,3n)¹⁶⁵Tm, ¹⁶⁷Er(p, γ)¹⁶⁸Tm, ¹⁶⁸Er(p,2n)¹⁶⁷Tm and ¹⁷⁰Er(p,3n)¹⁶⁸Tm, the nuclear cross section was measured for the first time. From the results obtained, the production yield and purity of the parent radioisotope ¹⁶⁵Tm were calculated to assess the optimal irradiation conditions. Several production tests with solid targets were performed to confirm these findings.

Keywords: Auger electrons; Cross sections; Erbium-165; Medical cyclotron; Proton irradiation; Solid targets; Targeted radionuclide therapy.