Production of high specific activity rhenium-186 via the 186W(d,2n)186Re nuclear reaction using pressed tungsten-186 metal targets and evaluation of separation methods

Rhenium-186 (t_1/2 = 3.72 d) is a highly desirable radionuclide that emits therapeutic β^- particles with a β^-_max energy of 1.07 MeV, allowing for a targeted tissue range of up to 3.6 mm. In addition, its 137 keV (8.6%) gamma emission makes it suitable for theranostic applications. Currently, low specific activity ¹⁸⁶Re is produced in a reactor via the ¹⁸⁵Re(n,g)¹⁸⁶Re nuclear reaction, but demand for high specific activity ¹⁸⁶Re for targeted radiotherapy applications can potentially be met using charged-particle activation of ¹⁸⁶W targets via the ¹⁸⁶W(d,2n)¹⁸⁶Re nuclear reaction.

A graphite-encased ¹⁸⁶W metal target (99.9% enriched) was prepared by uniaxially pressing ¹⁸⁶W metal powder between two layers of graphite flakes with 13.8 MPa of hydraulic pressure. The target was bombarded with 22 MeV deuterons for a total of 27 μAh, with an estimated incident deuteron energy of 19.5 MeV on the ¹⁸⁶W metal layer. Following a cool-down period to allow co-produced W-187 to decay, the target was dissolved using 30% H₂O₂ and then divided into two aliquots. Separation of the ¹⁸⁶Re product in these aliquots was evaluated using an Analig Tc-02 resin column procedure and a methyl ethyl ketone (MEK) solvent extraction procedure. The isolated ¹⁸⁶Re product was evaluated by radiolabeling a 222-MAMA-N-propionate ligand. Further studies were performed to optimize separation yield conditions by varying resin type, loading solution, and target mass.

An EOB ¹⁸⁶Re yield of 0.611 GBq (16.5 mCi) was obtained after a 27 μAh deuteron bombardment. We report a method for the production and separation of high specific activity ¹⁸⁶Re from the deuteron bombardment of graphite-encased ¹⁸⁶W metal targets. Both separation methods resulted in high recovery yields of ¹⁸⁶Re, which was then successfully used to radiolabel a 222-MAMA-N-propionate ligand.

Figure 1: HPLC gamma chromatogram of radiolabeling reaction mixture showing radiolabeled ¹⁸⁶Re- MAMA at 9 minutes and ¹⁸⁶ReO₄^- at 2.7 minutes (20-80 % H2O/MeCN in 20 minutes.