Tritium – Competitive Reaction in Cyclotrons F-18 Production – Regulatory Implications
Abstract of the technical paper/presentation presented at:
Meeting of the Task Force on Shielding Aspects of Accelerators, Targets and Irradiation Facilities
October 11, 2016
Canadian Nuclear Safety Commission
The Canadian Nuclear Safety Commission (CNSC) regulates many different types of accelerator facilities, as well as the possession and use of nuclear substances across Canada. In the last forty years, positron emission tomography (PET) has advanced rapidly and is becoming an indispensable imaging modality for evaluating cancer patients. Of the hundreds of positron-labelled radiotracers, 2-[18F]-fluoro-2-deoxy-D-glucose (FDG) is the most successful and widely used imaging agent in PET today. Canada is no exception; last year, a total combined 18F production of 1.37 PBq at the end of bombardment (EOB) was reported from the cyclotron facilities licensed by the CNSC.
In the last decade, several published papers have confirmed the presence of tritium in enriched (H218O) water via the competitive reaction 18O (p, t)16O during the production of 18F. In 2015, five Canadian cyclotron licensees were invited to participate in a study of tritium production conducted by the CNSC laboratory. The aim was to evaluate the levels of tritium produced by different types and models of cyclotron, under different operation conditions and with different enriched water suppliers.
A tri-carb (low background level) liquid scintillation counter was used to measure tritium activity in the samples. Some samples were found to have high contents of tritium and had to be diluted for analysis. A laboratory blank and a QC sample were also included in the measurement sequence for quality control. This study presents the results of the measurements. The measurements confirmed the presence of competitive reaction 18O (p, t)16O during the production of 18F, as well as the presence of tritium in non-irradiated enriched water. It also presents some of the possible regulatory implications.
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