Production, separation and evaluation of Tc99m and Mo99 from accelerator transmutation of Mo100

Objectives To demonstrate potential for translation to clinic of Tc99m and molybdenum-99 (Mo99) produced from linear accelerator-transmutated Mo100

Methods 1-mm natural molybdenum metal (9.63% abundance Mo100, Sigma) was irradiated in a stack of 20 1.25-cm discs at 20 MeV/10 kW. Tests to determine the most efficient dissolution solvent(s) for metal target and conversion to Na2MoO4 were performed. Acid mixtures studied were 50%w/v HNO3 (1), 50%v/v HNO3 (2), HNO3:H2SO4:H2O (5:3:2) (3), with or without heat. We possess solvent extraction generator technology previously in clinical use for fission-produced Mo99, and validated for low specific activity Mo99 from Mo98(n,γ)Mo99.

Results Mo99 yields were 1.7GBq and 4.6GBq. Optimization runs using 1-mm, 2.4cm diameter discs are in progress, with a focus on improved beam targets. Distribution of activity over individual discs (Fig 1A) correlated very closely to MCNP modeling, with disc10 at 54.2% and disc20 at 26.0% of activity of disc1 (versus 54.7, 29.4% for modeling). Nb95 and Nb96 impurities were seen (Fig 1B), presumably from Mo-96(γ,p)Nb-95 and Mo-97(γ,p)Nb-96 reactions. Efficiency of dissolution was 3>2>1, with complete dissolution by 3 obtained for a tranche of 12 discs (<1 hr, 90C). Product was confirmed as MoO3 by XRD. A clear colored solution was obtained after drying at low heat overnight and addition of 5M NaOH. When using 1, a film formed on the metal, impeding further dissolution. Solvent extraction gave relatively pure Tc99m as product (germanium spectroscopy, Fig 1C) though at low yields (highest extraction= 27%). Optimization of extraction is in progress. Reductive conversion appears to contribute to lower yields; extraction improved by addition of H2O2.

Conclusions Production chain shows good potential for clinical translation. Use of Mo99 isotopically-enriched targets should increase irradiation yields ten-fold and minimize radionuclidic impurities.

Research Support Health Sciences Centre Foundatio