High-yield, low-pressure [18O] water targets of titanium and niobium for F-18 production on MC-17 cyclotrons

Monte Carlo simulation and radiometric characterization of proton irradiated [18O]H₂O for the treatment of the waste streams originated from [18F]FDG synthesis process

The aim of this work is quantifying the radionuclidic impurities of the irradiated [(18)O]water originated by the [(18)F]FDG synthesis process, and characterizing, from a radioprotection point of view, the waste streams produced. Two samples of 2.4ml [(18)O]H(2)O, contained in two different target cells, have been irradiated with a proton current of 37μA in a PETtrace cyclotron for about one hour each; after irradiation, without performing any chemical purification process but waiting only for the (18)F decay, they have been transferred in two vials and measured by HPGe gamma spectrometry and, subsequently, by Liquid Scintillation Counting. Previously, Monte Carlo calculations had been carried out in order to estimate the radionuclides generated within the target components ([(18)O]H(2)O, silver body and Havar® foil), with the aim to identify the nuclides expected to be found in the irradiated water. Experimental results for the two samples, normalized to the same irradiation time, show practically the same value of tritium concentration (about 36kBq/ml) while gamma emitters activity concentrations exhibit a greater spread. Considering that tritium derives from water activation while other pollutants are caused by activated cell materials released into water through erosion/corrosion mechanisms, such a spread is likely to be attributable to differences in the proton beam shape and position (production of different natural circulation patterns inside the target and different erosion mechanisms of the target cell walls). Both tritium and the other radioactive pollutants exhibit absolute values of activity and activity concentrations below the exemption limits set down in EURATOM Council Directive 96/29.

Standardization of fluorine-18 manufacturing processes: new scientific challenges for PET

In [(18)F]fluoride chemistry, the minute amounts of radioactivity taking part in a radiolabeling reaction are easily outnumbered by other reactants. Surface areas become comparably larger and more influential than in standard fluorine chemistry, while leachables, extractables, and other components that normally are considered small impurities can have a considerable influence on the efficiency of the reaction. A number of techniques exist to give sufficient (18)F-tracer for a study in a pre-clinical or clinical system, but the chemical and pharmaceutical understanding has significant gaps when it comes to scaling up or making the reaction more efficient. Automation and standardization of [(18)F]fluoride PET tracers is a prerequisite for reproducible manufacturing across multiple PET centers. So far, large-scale, multi-site manufacture has been established only for [(18)F]FDG, but several new tracers are emerging. In general terms, this transition from small- to large-scale production has disclosed several scientific challenges that need to be addressed. There are still areas of limited knowledge in the fundamental [(18)F]fluoride chemistry. The role of pharmaceutical factors that could influence the (18)F-radiosynthesis and the gaps in precise chemistry knowledge are discussed in this review based on a normal synthesis pattern.

Electrochemical transfer of (18)F from (18)O water to aprotic polar solvent

Electrochemical transfer of (18)F(-) from enriched [(18)O]-water to pure acetonitrile was investigated to develop a simple and effective synthesis of (18)F-radiopharmaceuticals. The transfer of (18)F is composed of two steps: first step is electro-deposition on a graphite anode and the next step is electro-emission into pure acetonitrile by inversing the polarity of the electric tension. A sufficiently high fraction of the electro-emission, 73%, was achieved. The electrochemical transfer of (18)F to aprotic polar solvents without any additives, such as phase transfer catalysis, will make the synthesis of diverse (18)F-radiopharamceuticals simple and easy.

A grid-mounted niobium body target for the production of reactive [18F]fluoride

A small-volume grid-supported niobium target was constructed for the production of [18F]-fluoride on a CTI RDS 112 cyclotron. The inert properties of niobium metal have proven compatible with the superheated environment generated during proton irradiation. A grid support, constructed from aluminum, provides the necessary heat removal for high-power irradiations. The niobium and gird combination supplies reactive fluoride over an extended target lifetime.