Production, Purification and Availability of (211)At: Near Term Steps Towards Global Access

The promising characteristics of the 7.2-h radiohalogen (211)At have long been recognized; including having chemical properties suitable for labeling targeting vectors ranging from small organic molecules to proteins, and the emission of only one α-particle per decay, providing greater control over off-target effects. Unfortunately, the impact of (211)At within the targeted α-particle therapy domain has been constrained by its limited availability. Paradoxically, the most commonly used production method – via the (209)Bi(α,2n)(211)At reaction – utilizes a widely available natural material (bismuth) as the target and straightforward cyclotron irradiation methodology. On the other hand, the most significant impediment to widespread (211)At availability is the need for an accelerator capable of generating ≥28 MeV α-particles with sufficient beam intensities to make clinically relevant levels of (211)At. In this review, current methodologies for the production and purification of (211)At – both by the direct production route noted above and via a (211)Rn generator system – will be discussed. The capabilities of cyclotrons that currently produce (211)At will be summarized and the characteristics of other accelerators that could be utilized for this purpose will be described. Finally, the logistics of networks, both academic and commercial, for facilitating (211)At distribution to locations remote from production sites will be addressed.