Metodologia para calibração do detector de NaI(Tl) 3”x3” para medições in vivo em pacientes submetidos a radioiodoterapia e indivíduos ocupacionalmente expostos ao 131I

According to studies by the Instituto Nacional do Câncer (INCA), in recent years the incidence of thyroid cancer is the fastest growing in relation to other types. For the treatment is required the exact amount of 131I isotope for each patient resulting on manipulation of this isotope in nuclear medicine services by individuals who are considered occupationally exposed (OEI). This work aims to establish the methodology for calibration of the detection system used to determine the therapeutic activity of 131I, required to release the desired absorbed dose in the thyroid gland, as well as in monitoring OEI that manipulate this radionuclide in nuclear medicine services. This is one of the early stages of implementation of Laboratorio de Dosimetria Interna at the Centro Regional de Ciencias Nucleares do Nordeste (CRCN-NE). The detector system consists of a NaI(Tl) 3"x 3" associated with electronic devices and Genie 2000 software. Sources of 60Co, 137Cs and 133Ba were utilized for calibration. Firstly, measurements were carried out in non-exposed individuals for obtaining the Minimum Detectable Activity (MDA) and then Minimum Detectable Incorporation (MDI) and the Minimum Effective Dose Detectable (MEDD) were determined through biokinetic models provided by the ICRP 67 and edited by the AIDE software version 6 to workers and patients. The values for the MEDD were 3.57 x 10-2 mSv, 5.56 x 10-2 mSv and 10.7 x 10-2 mSv to 1, 7 and 14 days, respectively, after 131I incorporation by workers. As for patients, MEDD were 3.44 x 10-2 mSv, 5.63 x 10-2 mSv and 10.9 x 10-2 mSv for the same periods of time. It is applicable to the assessment of dose OEI, since it presents less than the recommended minimum of 1 mSv. The technique also has adequate sensitivity for evaluation of activity present in the thyroid of patients with thyroid dysfunction.