Nuclear medicine physics
Innovative methodology for intercomparison of radionuclide calibrators using short half-life in situ prepared radioactive sources
An original radionuclide calibrator method for activity determination is presented. The method could be used for intercomparison surveys for short half-life radioactive sources used in Nuclear Medicine, such as99mTc or most positron emission tomography radiopharmaceuticals.
By evaluation of the resulting net optical density (netOD) using a standardized scanning method of irradiated Gafchromic XRQA2 film, a comparison of the netOD measurement with a previously determined calibration curve can be made and the difference between the tested radionuclide calibrator and a radionuclide calibrator used as reference device can be calculated. To estimate the total expected measurement uncertainties, a careful analysis of the methodology, for the case of99mTc, was performed: reproducibility determination, scanning conditions, and possible fadeout effects. Since every factor of the activity measurement procedure can influence the final result, the method also evaluates correct syringe positioning inside the radionuclide calibrator.
As an alternative to using a calibrated source sent to the surveyed site, which requires a relatively long half-life of the nuclide, or sending a portable calibrated radionuclide calibrator, the proposed method uses a source preparedin situ. An indirect activity determination is achieved by the irradiation of a radiochromic film using 99mTc under strictly controlled conditions, and cumulated activity calculation from the initial activity and total irradiation time. The irradiated Gafchromic film and the irradiator, without the source, can then be sent to a National Metrology Institute for evaluation of the results.
The methodology described in this paper showed to have a good potential for accurate (3%) radionuclide calibrators intercomparison studies for99mTc between Nuclear Medicine centers without source transfer and can easily be adapted to other short half-life radionuclides.