A comparison of four radionuclide dose calibrators using various radionuclides and measurement geometries clinically used in nuclear medicine

Purpose: Reliable quantification of radioactivity in nuclear medicine is becoming increasingly important in various therapeutic applications requiring a high accuracy of nuclear medicine measuring equipment, such as radionuclide calibrators. In this study the accuracy of four different radionuclide calibrators was assessed for Tc-99m,In-111,Ga-68 and F-18 for measurement geometries clinically used.

Methods: Syringes and vials were prepared with a reference activity using a stock solution of which the activity concentration was determined using gamma-ray spectroscopy. The accuracy of four different radionuclide calibrator systems, ISOMED 2000, ISOMED 2010, VIK-202 and Capintec CRC-25R, was assessed by comparing the measured activity to the reference activity.

Results: Deviations in measured activity from reference values were found up to 12.5%, 32.0%, 29.0% and 12.6% for Tc-99m,In-111,Ga-68 and F-18, respectively. For Ga-68 all radionuclide calibrators systematically overestimated the activity by 10-20%. For(111)In, large differences in activity measurements were observed between different source geometries, in particular between syringes and vials. Deviations between radionuclide calibrator systems were found up to 11.8%, 44.4%, 14.4% and 8.7% for( 99m)Tc,In-111,Ga-68 and F-18, respectively. When comparing similar syringe types of different brands filled with identical stock solution volume, deviations up to 1.8%, 5.8%, 10.2% and 3.2% were found for Tc-99m,In-111,Ga-68 and F-18.

Conclusion: Substantial deviations in measured activity were found for all radionuclides and radionuclide calibrators, which may result in erroneous activity dosing and image quantification. This underlines the importance of thorough validation of radionuclide calibrators for all measurement geometries and radionuclides clinically used.