Design and evaluation of an external high-current target for production of 211At

This report presents the design and testing of an external target system for clinical-scale production of 211At on the Scanditronix MC-50 cyclotron at the University of Washington Medical Center. While other 211At production sites have typically employed an internal target, an external target setup was deemed necessary at our facility since the cyclotron's main application is for cancer patient treatment via fast neutron therapy. The challenge was that previous external 211At targets demonstrated reduced yields when compared to internal target systems. The target developed in this study has been used in more than 100 irradiations. From those irradiations 211At saturated yields of 181 ± 16 MBq/μA and 241 ± 17 MBq/μA at 28.0 and 29.0 MeV, respectively, were obtained. Importantly, consistent yields were observed over the 25–60 μA range of irradiation currents evaluated. With a recent production in excess of 4 GBq 211At for a 29.0 MeV, 58 μA, 4-hour irradiation, this external target system has demonstrated its potential for producing clinically relevant quantities of 211At.