PNNL

Abstract

Cyclotron-produced astatine-211 (211At, t1/2 = 7.214 h) shows tremendous promise in targeted alpha therapy (TAT) applications due to its attractive half-life and its nearly simultaneous branched alpha decay (211At (5.87 MeV, 41.8%) and 211Po (7.45 MeV, 58.2%)). Astatine-211 is produced using alpha beam bombardment of naturally monoisotopic bismuth metal (209Bi) via the (a, 2n) reaction. In order to isolate the small mass of 211At (10-20 ng) from several grams of acid-dissolved Bi metal, we employ a solvent extraction process using diisopropyl ether (DIPE). As the solvent extraction process is complex and time consuming, we have developed a fluidic workstation that can perform the method autonomously. In lieu of aqueous / organic phase mixing in a stirred vessel followed by manual phase separation using a transfer pipette, the workstation employs two pumps to concurrently deliver the aqueous and organic phases to a mixing tee and in-line phase mixer. The mixed phases are routed to a phase settling reservoir, where they gravity settle. Finally, each respective phase is withdrawn into its respective pump. However, development of a phase boundary sensor, placed in tandem with the phase settling reservoir, was necessary to communicate to the system when withdrawal of the aqueous phase was complete (i.e., the intersection of the two phases was located). The development and optimization of the autonomous solvent extraction system is described, and the 211At yields from several clinical-level 211At processing runs is reported.