title: Iodine-123 assay using a radionuclide calibrator.
abstract: Iodine-123 (123I), an accelerator-produced radionuclide, gained wide acceptance recently in medical applications. Radionuclide dose calibrators are commonly used to assay radioactivities of radiopharmaceuticals, and should be maintained to read within +/- 5%, both for constancy and accuracy. Radionuclidic impurities present in commercial 123I preparations may produce an assay error larger than 10%. The type and quantity of impurities depend on the mode of production of 123I. The impurities can be reduced by either increasing the energy of the proton beam (over 60 MeV) and using the 127I (p,5n) 133Xe leads to 123I indirect reaction or using lower energies and highly enriched (better than 99%) 124Te (or 122Te) target for the direct production of 123I via 124Te (p, 2n) 123I or 122Te (d, n) 123I. A survey of radionuclide calibrators was undertaken to investigate the extent of the 123I assay error due to impurities present in commercially available preparations of 123I. Results from 24 calibrators indicate that the activity of a (p, 2n) 123I capsule is overestimated on average by 22% two half-lives after calibration time, while the activity of a (p, 5n) 123I capsule remains within the accuracy of the radionuclide calibrator of +/- 5%. The 124I fraction increases significantly with time during the useful life of a (p, 2n) 123I capsule introducing large 123I assay errors.
mesh_terms: D002138:Calibration; D007457:Iodine Radioisotopes; D009683:Nuclear Medicine / Q000592:standards*; D011851:Radioactivity
chemical_list: D007457:Iodine Radioisotopes