Tehran University of Medical Sciences
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Davood Beiki

Determination of radiation dose rates and urinary activity of patients received sodium iodide-131 for treatment of differentiated thyroid carcinoma

Authors: Beiki D, Shahhosseini S, Dadashzadeh S, Eftekhari M, Tayebi H, Moosazadeh-Rashti G,
Keywords: Sodium iodide-131; Thyroid carcinoma; Instantaneous dose rate; Urinary excretion
Iran J Nucl Med , Vol.12, No.1, 2004,Page:1-13

Sodium Iodide-131 is administrated for treatment of hyperthyroidism and thyroid cancer. Iodine-131 has multiple routs of excretion (Urine, saliva, sweat, milk, feces, exhalation) from the body. Patients receiving Sodium Iodide-131 therapy exposes other persons and the environment to unwanted radiation and contamination. The major source of radiation dose from administration of Iodine-131 is external radiation, also there is a potential for exposure via contamination. Precautions are necessary to limit the radiation dose to family members, nursing staff and members of public and waste treatment workers to less than 1mSv. Patients received Sodium Iodide-131 may come into close contact with other persons. In order to derive appropriate recommendations, dose rates were measured from the anterior mid-trunk of 29 patients in the upright position within 15 minutes post-dose administration at 3 meters and just before they left the nuclear medicine department at 0.5, 1 and 3 meters. We have also measured urinary iodide excretion in 29 patients to estimate Sodium Iodide-131 urinary excretion pattern in Iranian patients. Based on results, the maximum cumulative dose to nursing staff was on third day (Leaving day) still less than recommended dose by ICRP. The cumulative dose of family members will be more but regarding the time and distance in close contact it will also be less than recommended dose by ICRP. Radiation dose rate was decreased significantly on third day. The urinary excretion patterns in all patients were similar. The urinary excretion rate-time curve in all patients showed multiple peaks due to retention and redistribution of Iodine-131 or entrohepatic cycle of radioiodinated thyroid hormones, which didn’t allow calculation of urinary excretion rate constant. The results also showed that 67 hours post administration of Sodium Iodide-131 about 70% of radiopharmaceutical was excreted through urine, 28% physically decayed or eliminated through other biological route