Monte Carlo prediction and experimental characterisation of long-lived waste byproducts arising from cyclotron production of zirconium-89 utilising a commercially available yttrium foil.

Abstract

Zirconium-89 is presently undergoing pre-clinical investigation for its potential application as a positron emission tomography (PET) theranostic radioisotope. A critical consideration in the increasing number of trials and eventual clinical implementations is a comprehensive understanding of the radioactive waste byproducts and their quantification. This study focuses on the investigation and characterisation of the waste isotopes generated during the production of Zirconium-89, employing a combination of Geant4 Monte Carlo simulation and experimental methodologies utilising commercially obtainable starting materials from Thermofisher. Post cyclotron production samples of waste were taken and measured using a high purity germanium detector. Subsequent spectrum analysis consistently revealed the presence of the following isotopes in units of kBq per GBq of Zirconium-89 produced: cobalt-56 (13 ± 2, 14 ± 2, 15 ± 1), cobalt-57 (0.087 ± 0.004, 0.097 ± 0.004, 0.086 ± 0.007), rhenium-183 (2.61 ± 0.06, 3.29 ± 0.06, 2.47 ± 0.09), scandium-48 (27 ± 0.9, 21.1 ± 0.4), yttrium-88 (0.67 ± 0.06, 1.1 ± 0.4, 0.73 ± 0.06) and zirconium-88 (90 ± 5, 1340 ± 60, 35 ± 2). All the waste isotopes were able to reasonably be estimated using Geant4 Monte Carlo simulations or the deviation was able to be justified. The repeatability and predictability of isotopes and activities will enable informed decision-making regarding storage and disposal procedures in accordance with local legislative requirements.