Intercomparison of 99mTc, 18 F and 111In activity measurements with radionuclide calibrators in Belgian hospitals

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 Tc-99m, F-18 and In-111 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 Tc-99m and In-111, and 21 calibrations for F-18. For each radionuclide, 3 ml of stock solution was measured in two clinical geometries: a 10 ml glass vial and a 10 ml syringe. The initial activity was typically 100 MBq for Tc-99m, 15 MBq for In-111 and 115 MBq for F-18. 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 99 mTc and F-18, since most radionuclide calibrators ( > 70%) were accurate within +/- 5% of the reference value. Nevertheless, some devices underestimated the activity by 10-20%. Conversely, In-111 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.