¹³⁵La as an Auger-electron emitter for targeted internal radiotherapy

Abstract

¹³⁵La has favorable nuclear and chemical properties for Auger-based targeted internal radiotherapy. Here we present detailed investigations of the production, emissions, and dosimetry related to ¹³⁵La therapy. ¹³⁵La was produced by 16.5 MeV proton irradiation of metallic natBa on a medical cyclotron, and was isolated and purified by trap-and-release on weak cation-exchange resin. The average production rate was 407 ± 19 MBq µA−1 (saturation activity), and the radionuclidic purity was 98% at 20 h post irradiation. Chemical separation recovered > 98 % of the ¹³⁵La with an effective molar activity of 70 ± 20 GBq µmol−1. To better assess cellular and organ dosimetry of this nuclide, we have calculated the x-ray and Auger emission spectra using a Monte Carlo model accounting for effects of multiple vacancies during the Auger cascade. The generated Auger spectrum was used to calculate cellular S-factors. ¹³⁵La was produced with high specific activity, reactivity, radionuclidic purity, and yield. The emission spectrum and the dosimetry are favorable for internal radionuclide therapy.