Development and calibration of a portable detection system for in vivo monitoring of 131I incorporation by humans

131I is one of the most frequently used radionuclides for diagnosis and therapy of thyroid diseases in nuclear medicine. Its increasing use for medical purposes creates a demand for feasible methodologies applied to the control of internal exposure by workers. In vivo monitoring of 131I incorporation is of great value for the evaluation of occupational exposure during its medical application and also in the case of accidents and incidents in nuclear power plants for the monitoring of workers and population. This work presents the development of a portable device specially designed for in vivo measurement of 131I in the thyroid. It is also presented the results of the calibration performed in different nuclear medicine centers where 131I is routinely manipulated for therapeutic purposes. The equipment consists in a NaI(Tl)3''x3'' detector installed in a lead collimator and assembled on a tripod. The detection system was calibrated with the IRD-Neck-Thyroid phantom for the determination of the calibration factors for direct in vivo quantification of 131I in the thyroid. In order to evaluate the applicability and limitations of the system, committed effective doses associated to the minimum detectable activities were calculated using current biokinetic and dosimetric models available in the literature. Dose detection limits have shown to be far below 1 mSv for the most likely incorporation scenarios. (author)