Bulk production and evaluation of high specific activity 186g Re for cancer therapy using enriched 186 WO 3 targets in a proton beam.

INTRODUCTION: Rhenium-186g (t1/2 = 3.72 d) is a β- emitting isotope suitable for theranostic applications. Current production methods rely on reactor production by way of the reaction 185 Re(n,γ)186g Re, which results in low specific activities limiting its use for cancer therapy. Production via charged particle activation of enriched 186 W results in a 186g Re product with a higher specific activity, allowing it to be used more broadly for targeted radiotherapy applications. This targets the unmet clinical need for more efficient radiotherapeutics.

METHODS: A target consisting of highly enriched, pressed 186 WO3 was irradiated with protons at the Los Alamos National Laboratory Isotope Production Facility (LANL-IPF) to evaluate 186g Re product yield and quality. LANL-IPF was operated in a dedicated nominal 40 MeV mode. Alkaline dissolution followed by anion exchange chromatography was used to isolate 186g Re from the target material. Phantom and radiolabeling studies were conducted with the produced 186g Re activity.

RESULTS: A 186g Re batch yield of 1.38 ± 0.09 MBq/μAh or 384.9 ± 27.3 MBq/C was obtained after 16.5 h in a 205 μA average/230μA maximum current proton beam. The chemical recovery yield was 93% and radiolabeling was achieved with efficiencies ranging from 60-80%. True specific activity of 186g Re at EOB was determined via ICP-AES and amounted to 0.788 ± 0.089 GBq/μg (0.146 ± 0.017 GBq/nmol), which is approximately seven times higher than the product obtained from neutron capture in a reactor. Phantom studies show similar imaging quality to the gold standard 99m Tc.

CONCLUSIONS: We report a preliminary study of the large-scale production and novel anion exchange based chemical recovery of high specific activity 186g Re from enriched 186 WO3 targets in a high-intensity proton beam with exceptional chemical recovery and radiochemical purity.