Abstract
This study investigates the characteristics of individual dose formation in Category A personnel (n = 20) working with radioactive iodine-131 (¹³¹I) under conditions of radionuclide therapy and diagnostics. The aim of the study was to assess the informative value of individual dosimetric monitoring for the analysis of both external and internal exposure in the real clinical practice of the Center of Nuclear Medicine and Oncology of the Abai Region. Based on a retrospective analysis of individual dosimetric monitoring data and in vivo spectrometry measurements, the variability of ¹³¹I activity in the thyroid gland of personnel and its contribution to the annual effective dose were evaluated. It was demonstrated that, when radiation safety regulations are complied with, occupational dose levels remain significantly below established regulatory limits. At the same time, differences in internal exposure indicators were found to be more strongly associated with individual clinical and physiological characteristics of thyroid function than with the conditions of professional activity. The obtained results demonstrate that individual dosimetric monitoring can be considered not only a regulatory tool but also an analytical instrument that enables deeper interpretation of dose formation mechanisms and supports the justification of further optimization of radiation protection systems in accordance with the ALARA principle.