Production, purification and availability of At: Near term steps towards global access.

The promising characteristics of the 7.2-h radiohalogen 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 At within the targeted α-particle therapy domain has been constrained by its limited availability. Paradoxically, the most commonly used production method - via the Bi(α,2n)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 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 At. In this review, current methodologies for the production and purification of At - both by the direct production route noted above and via a Rn generator system - will be discussed. The capabilities of cyclotrons that currently produce 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 At distribution to locations remote from production sites will be addressed.