Optimum radioactivity yield of Zirconium-89 radionuclide applicable for radioimmuno-PET imaging

Abstract

Since Zirconium-89 (89Zr or Zr-89) decays by emitting positron with a half-life of 78.4 hours, it has been suggested as a diagnostic radioisotope for cancer. Normally, Zirconium-89 is generated by irradiating an enriched yttrium-89 (89Y or Y-89) target with protons via 89Y(p,n)89Zr nuclear reaction. Optimum proton energy employed to produce high Zr-89 yield and low radioactive impurities is required to be determined so that it meets the requirements for clinical use. In this work, a Y-89 target was bombarded with variable proton energies ranging from 11 to 30 MeV. The Zr-89 radioactivity yields dan radioactive impurity yields were calculated using the CalcuYield code, in which the proton beam current was set to be 1 μA while the target was bombarded for 1 hour. Based on the CalcuYield calculations, the radioactivity yield of Zr-89 produced by 11 MeV protons was 41.18 MBq/μAh, whereas the yield increased significantly to 166.76 MBq/μAh when the Y-89 target was bombarded with 30-MeV protons. The higher Zr-89 radioactivity yields also resulted in higher radioactive impurities, which could be of concern when applied to patients. By assuming that the radioactive impurities came from proton interactions with the Y-89 target, it was found that the 11 and 13 MeV proton-bombarded Y-89 target resulted in no radioactivity impurities. The radioactive impurities became significantly high when greater than 18 MeV protons were employed. These estimated results can be employed as a benchmark for the coming Zr-89 radionuclide generation applicable for radioimmuno-PET imaging.