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UBC Theses and Dissertations

Analysis of radioisotopes generated during the cyclotron production of Tc-99m Stothers, Laurel Anne


Technetium-99m (⁹⁹mTc) is the most commonly used radioisotope in nuclear medicine due to its favourable half-life and single-energy gamma emission. At present, it is obtained largely from the decay of molybdenum-99 (⁹⁹Mo) in ⁹⁹Mo/⁹⁹mTc generators. However, the ⁹⁹Mo is produced from enriched uranium in aging nuclear reactors which are prone to closure and risk disrupting ⁹⁹mTc production. To stabilize the global supply of ⁹⁹mTc, the ¹⁰⁰Mo(p,2n)⁹⁹mTc reaction has been investigated as an alternative method of production. This method makes use of small medical cyclotrons as opposed to ⁹⁹Mo/⁹⁹mTc generators and has already been shown to generate high yields of ⁹⁹mTc. However, irradiation of the ¹⁰⁰Mo target produces other radioisotopes which either impact purity of the ⁹⁹mTc product or constitute radioactive waste. The objective of this thesis was to determine the identity and activity of all radioisotopes produced during cyclotron-based ⁹⁹mTc production, in order to assess whether this alternative method is viable for use in nuclear medicine. To address the thesis’ objective, gamma-ray spectroscopy was performed on numerous ⁹⁹mTc product and radioactive waste samples. Gamma-ray spectroscopy was used in both avenues of investigation to identify the radioisotopes present in the samples and to quantify the activities of those identified. For the study on ⁹⁹mTc product samples, this information was used to determine the purity of the product. Then, the potential patient dose increase due to these product impurities was calculated. For the subsequent study on waste produced, activity and effective half-life of the waste was determined in order to evaluate potential difficulties associated with managing waste accumulation over time. The sources of radioisotopes found in the waste were identified to develop strategies for waste reduction. Analysis showed that the cyclotron-produced ⁹⁹mTc was highly pure, with an average radionuclidic purity of 0.9997%. Moreover, impurities that were present in the product contributed a patient dose increase of only 0.7% at expiration. For the waste samples, 50 radioisotopes were identified with a total activity of 0.059±0.002GBq at end of beam per 1GBq of ⁹⁹mTc produced. They came mainly from target impurities. Overall, this investigation suggests that cyclotron-produced ⁹⁹mTc is viable for clinical use.

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