[en] The aim of this study is to establish the methodology for calibration of the detection system to be used in determining the therapeutic activity of ¹³¹I required to release desired absorbed dose in the thyroid gland . This step is critical to the development of a protocol for individualized doses. The system consists of a detector of NaI (Tl ) 3'x3' coupled to software Genie 2000. We used the calibration sources of ⁶⁰Co , ¹³⁷Cs and ¹³³Ba. We obtained the straight calibration system, with sources ⁶⁰Co and ¹³⁷Cs. Subsequently , the detector was calibrated using a thyroid phantom-neck designed and produced by the IRD / CNEN with known activity of ¹³³Ba standard solution containing 18.7 kBq (on 09/24/12) evenly distributed. He was also calibrated with other thyroid- neck phantom model 3108 manufactured by Searle Radigraphics Ind., containing a liquid source of ¹³¹I ( 7.7 MBq ). Five measurements were performed during 5 minutes for three different distances detector-simulator and calculated the corresponding calibration factors . The values of the calibration factors found for the simulator made by IRD and Searle Radigraphics Ind. for the distances 20, 25 and 30 cm were 0.35 , 0.24, 0.18, 0.15 , 0.11, 0, 09 , respectively. With the detection system properly calibrated and the calibration factors established, the technique is suitable for the evaluation of diagnostic activities of ¹³¹I incorporated by hyperthyroid patients. (author)