Chemical properties

In the periodic table astatine is situated at the boundary of halogens and metalloids, i.e., partly behaves like a halogen and partly like a metal. This requires dedicated labelling strategies REF.

Nuclear properties

At-211 decays with 7.214(7) h half-life. It decays by 58.2% electron capture to short-lived Po-211 (T_1/2 = 0.516(3) s) that decays in turn with 100% ɑ emission to stable Pb-207. Moreover, At-211 decays by 41.8% ɑ emission to quasi-stable Bi-207 (T_1/2=31.6 years; only 26 Bq Bi-207 per 1 MBq of At-211 after decay of the latter) that decays in turn to stable Pb-207. Including its short-lived Po-211 daughter, the cumulative ɑ emission is 100% per At-211 decay with an average ɑ energy of 6.78 MeV.

At-211 emits X rays, notably K_α at 78 keV (33.1(5)%) and K_β at 90 keV (9.06(5)%). These energies enable SPECT-imaging, preferably with medium energy collimators REF and tungsten collimator to avoid X ray fluorescence from lead.

Moreover, At-211 and its daughter Po-211 in equilibrium emit weak γ rays at 567.7 keV (0.31%), 687.0 keV (0.26%) and 897.8 keV (0.32%).

The mean ɑ energy per decay is 6785 keV, the mean recoil energy (of Bi-207 or Pb-207 recoils respectively) is 131 keV, the mean electron energy per decay is 3 keV, and the mean photon energy per decay is 43 keV.

Production

At-211 is produced by ɑ-particle irradiation of metallic Bi-209 targets at the cyclotrons at ARRONAX, Rigshospitalet (in partnership with DTU) or CERAD facility in NCBJ. A good control of the beam energy allows to monitor the amount of co-produced At-210. In particular, ARRONAX is now using an internal target system that allows to use optimal beam energies ranging for 28 MeV up to 30 MeV.

Distribution

The radiochemical separation is performed at ARRONAX, at the Hevesy Laboratory of DTU or at the CERAD facility of NCBJ by dry distillation. The activity will be shipped from end facility to the users as irradiated targets, scraped bismuth (more compact and easier to handle both sides), At-211 in chloroform solution or dry residue (preferred form).

Examples of use

• Clinical trials with At-211-radioimmunotherapy have been performed in the past and are ongoing. For example, there is one on NaAt for thyroid cancer - NCT05275946 - in Osaka (Japan) and another one PSMA-5 At-211 for prostate cancer - NCT06441994 - at Osaka (Japan).
• Several clinical trials are in preparation at ICO in Nantes (France) on superficial bladder cancer, at ICNAS (Portugal) on glioblastoma, at Institut Jules Bordet (Belgium) on TNBC and at UMC Utrecht (The Netherlands) on the treatment of neuroblastoma