Cyclotron production of ⁶⁸Ga using a solution target

Objectives To develop an efficient method for the production of ⁶⁸Ga with a solution target using a medium energy cyclotron.

Methods A solution target was designed and constructed with dual foils of Al (0.20 mm) and Havar (0.038 mm) separated by helium cooling to degrade the PETtrace cyclotron proton energy to ~14 MeV. The solution target insert (1.6 mL) was made of Ta and designed with enhanced heat exchange. The target was operated as a closed system. ⁶⁸Zn (99.23% isotopic enrichment) was dissolved in concentrated nitric acid, evaporated to dryness, and reconstituted with dilute nitric acid to form 1.7 M ⁶⁸Zn nitrate in 0.2N nitric acid as target solution. After 30 min of proton irradiation at 20 μA, the target solution was passed through a cation exchange column (AG-50W-X8, 1.3 g), which efficiently trapped both ⁶⁸Zn and ⁶⁸Ga. ⁶⁸Zn was subsequently eluted with 30 mL of 0.5M-HBr in 80% acetone without any measurable loss of ⁶⁸Ga. The AG column was rinsed with 5 mL water to remove the HBr-acetone solution. ⁶⁸Ga was eluted with 7 mL of 3N HCl solution with > 96 % elution efficiency. The radionuclidic purity was determined on an HPGe detector. Additionally, a Dionex HPLC system with post-column addition of 4-(2- pyridylazo) resorcinol and UV-detection was employed to analyze for non-radioactive metal contaminants.

Results The product yield was 1.98-2.10 GBq (53.4-56.8 mCi) decay-corrected at EOB with processing time of ~30 min. The radionuclidic purity of ⁶⁸Ga was found to be >99.9%, with the predominant contaminant being ⁶⁷Ga. The HPLC analysis showed Fe, Cu and Zn concentrations < 3 μg / mL. The production yield of ⁶⁸Ga can be further increased by increasing ⁶⁸Zn concentration in the target solution and extending irradiation time.

Conclusions A simple and efficient method of ⁶⁸Ga production was developed using a medium energy cyclotron and a solution target. The developed methodology offers a cost effective alternative route to ⁶⁸Ga in comparison with ⁶⁸Ge-based ⁶⁸Ga generators.

Research Support This work was supported by DOE (DE-SC0008947).