Isolation of At-211 by Dry-distillation under Oxidative Conditions for Targeted Alpha Therapy in Osaka University

Astatine (At)-211 is one of the most promising radionuclides for the targeted alpha therapy (TAT). In Osaka University, we have recently started the collaborative project for the TAT using 211At which can be produced in nuclear reactions using an accelerator. At present, cyclotron production, chemical separation, radiopharmaceuticals preparation, and pre-clinical trials of 211At are under study. In this contribution, our cyclotron production and chemical purification of 211At are presented. Astatine-211 was produced in the 209Bi(α, 2n)211At reaction at Research Center of Nuclear Physics (RCNP), Osaka University. A thin metallic Bi target was bombarded by 28.2-MeV 4He2+ beam with 0.5-1 particle μA for a few hours. The Bi target was set at 45o to the beam axis in an irradiation chamber. Beam energy was adjusted to avoid simultaneous synthesis of 210At decaying into highly toxic 210Po. After the irradiation, dry distillation was carried out with a simplified distillation apparatus to isolate 211At from the target materials . We used mixed helium and oxygen gas and also added a moisture content in the distillation system to yield oxidized At species which are easily transported, trapped, and dissolved in a small volume of distilled water. The irradiated Bi target was heated at 840oC. Vapored At species were transported to a Teflon tube cooled with ice water. During accumulation of 211At in the trap, a trapped amount of 211At was monitored with a CdTeZn detector. After a few tens of minutes, trapped 211At was stripped with 100 μL of distilled water at a flow rate of 250 μL/min. The radioactivity of 211At was determined by γ-ray spectrometry using a Ge detector. The 211At solution was supplied to pharmaceutical preparations, pre-clinical tests, and/or our chemical analysis. Recovery yield of 211At was 70-80% under optimum conditions. The separation time was typically within 30 min. In the symposium, results on our chemical analysis will be also presented.