Simulations and measurements of radionuclide calibrator response

In nuclear medicine, radiopharmaceuticals are administered to the patient to diagnose or treat various diseases. The radioactive activity of these radiopharmaceuticals is measured using a radionuclide calibrator. In this study, the response of a radionuclide calibrator in different measurement conditions was studied. Code system PENELOPE (2018) that applies Monte Carlo methods in electron and photon transport simulation was used to investigate the response as a function of photon energy emitted by the source, source location, source volume and source container type. These calculated results were compared to corresponding experimental results. Overall, the computational results conformed well with the experimental results. The computational energy-response followed a similar trend to the efficiency curve extracted from the manual of Capintec CRC-25R radionuclide calibrator. The response of the calibrator to a Tc-99m source as a function of both vertical and horizontal displacement was inspected, and the results indicated a cubic and exponential trend, respectively. In both cases, results present that there is an agreeing optimal depth range (14 - 23 cm) at which the source should be located. Within this range, the variation in response remains below 2 %. Furthermore, the central axis of the chamber was deemed horizontally optimal for measurements. In the radius range 0 - 2.1 cm, experimental results showed an increase of 4 % relative to the centre position. Corresponding calculated results presented an increase of about 3 %. The response as a function of volume and container type was calculated for Tc-99m and I-123 source, respectively. In the case of volume-response, computational results presented a decrease of around 0.5 % for volumes between 2 to 5 ml in a plastic syringe. Experimental methods showed a corresponding decrease no greater than 0.8 %. Measuring response in a 15C transparent glass vial instead of a 3 ml plastic syringe, showcased that the response is only 81 % and 75 % of that in the syringe in simulated and experimental results, respectively