Cyclotron Production For The Radiometal Zirconium-89 With An IBA Cyclone 18/9 And COSTIS Solid Target System (STS)

The development of biological targeting agents such as proteins, peptides, antibodies and nanoparticles with a range of biological half-lives demands the production of new radionuclides with half-lives (physical) complementary to these biological properties. Zirconium-89 (Zr-89) is a promising radionuclide for development of new immuno-PET agents due to its convenient half-life of 78.4 h, beta(+) emission rate of 23%, low maximum energy of 0.9 MeV resulting in good spatial resolution, stable daughter isotope of Yttrium-89 (Y-89) and favorable imaging characteristics, with only one significant gamma-line of 909 keV emitted during decay alongside the 511 keV positron photons(1). Our aim was to prove that isotopically pure Zr-89 could be produced in an IBA Cyclone 18/9 cyclotron equipped with a COSTIS STS using the Y-89(p,n)Zr-89 reaction and optimise the yield by reducing the beam degrader thickness without producing either Zr-88 or Y-88. The degradation of the beam energy with 400 and 500 mu m thick Niobium foils were achieved without overheating problems with 2-3 hours long irradiation times. From repeated measurements of activity, it was clear that there is a bi-exponential decay of radioactivity due to the short lived Zr-89m and Zr-89. The measured half-life of the longer lived radionulide was consistent with value for Zr-89. The energy spectrum from Zr-89 had energy peaks at 511 keV and 909 keV and was consistent with Zr-89. Production of Zr-89 with 500 mu m thick Niobium beam degrader (E-p = 9.8 MeV) was achieved, without producing either Zr-88 or Y-88. It was necessary to wait at least 4 hours before measuring the activity and decay correct in order to calculate the Zr-89g activity at the end of cyclotron production. Degrading the proton beam to 10 MeV produces radionuclidically pure Zr-89 with yields from 8 to 9 MBq/mu Ah. Whilst this is enough for pre-clinical use, the yield is not enough for either clinical use or commercial supply. Using thinner beam degraders to increase the proton beam energy increases the radionuclidic yield but it is not yet possible to exclude the presence of radionuclidic impurities.