ABSTRACT
TOPAS MC software was used to model the efficiency of a coaxial p-type HPGe detector, type GX9023 from Canberra. The model was validated by comparing experimental efficiencies with efficiencies calculated by TOPAS MC simulations. Three different geometries of radionuclide sources, placed at different heights from the detector endcap, were used to validate the model. The imposed criteria of 5% relative difference was met for a range of radionuclides and gamma-ray energies. As a result, the created detector model with TOPAS MC was considered validated.
ABSTRACT
This study presents current status of performance of radiopharmaceutical activity measurements using radionuclide calibrators in Belgium. An intercomparison exercise was performed among 15 hospitals to test the accuracy of 99mTc, 18F and 111In activity measurements by means of radionuclide calibrators. Four sessions were held in different geographical regions between December 2013 and February 2015. The data set includes measurements from 38 calibrators, yielding 36 calibrations for 99mTc and 111In, and 21 calibrations for 18F. For each radionuclide, 3â¯ml of stock solution was measured in two clinical geometries: a 10â¯ml glass vial and a 10â¯ml syringe. The initial activity was typically 100â¯MBq for 99mTc, 15â¯MBq for 111In and 115â¯MBq for 18F. The reference value for the massic activity of the radioactive solutions was determined by means of primary and secondary standardisation techniques at the radionuclide metrology laboratory of the JRC. The overall results of the intercomparison were satisfactory for 99mTc and 18F, since most radionuclide calibrators (>70%) were accurate within ±5% of the reference value. Nevertheless, some devices underestimated the activity by 10-20%. Conversely, 111In measurements were strongly affected by source geometry effects and this had a negative impact on the accuracy of the measurements, in particular for the syringe sample. Large overestimations (up to 72%) were observed, even when taking into account the corrections and uncertainties supplied by the manufacturers for container effects. The results of this exercise encourage the hospitals to perform corrective actions to improve the calibration of their devices where needed.
