Metrological characterization of a NaI(Tl) well counter for activity estimation prior to in vitro 131I dosimetry measurements for Nuclear Medicine patients in Nicaragua, period 2022-2023.

Abstract

This research arose as a need to guarantee the quality of health to the Nicaraguan population according to the Plan to combat poverty and human development for 2022-2026. This research was focused on the dosimetry of nuclear medicine patients nationwide treated with 131I. The objective was to metrologically characterize a NaI(Tl) well counter to measure the activity in the patient’s blood to estimate doses in bone marrow or other organs. An iodine sample that was measured in a HPGe counter was used as a standard to achieve traceability to international standards. The study was cross-sectional in nature and focused on finding the correlation between the input stimulus (gamma radiation) and the output response of the well counter, measured in count rate kCPS (CPS, Counts per Second). Additionally, the response to the geometry of the sample, its energy and concentration was studied. The sensitivity obtained was 36.67% of the standard value measured in kBq. This result implies that, using the test method of this research, for each iodine sample subjected to counting (kCPS), when divided by the sensitivity, the activity value in kBq is obtained, with an estimated (combined) uncertainty of less than 10% of the measured activity value. This is based on the fact that for calibration, the uncertainty of the standard is 5%, which is metrologically acceptable for traceability. In summary, the findings indicate that the well counter used in this research has the necessary accuracy for its use in determining activities for dose calculations in bone marrow or other organs of interest through free access software.