Radiation dose rates from patients receiving iodine-131 therapy for carcinoma of the thyroid

We have combined whole-body dose rate measurements taken from 86 thyroid cancer patients after radioiodine administration with published data on nursing and social contact times to claculate the cumulative dose that may be received by an individual in contact with a patient. These dose estimates have been used to calculate restrictions to patients' behaviour to limit received doses to less than 1 mSv. We have also measured urinary iodine excretion in 19 patients to estimate the potential risk from the discharge of radioiodide into domestic drainage system. The dose rate decay was biexpotential for patients receiving radioiodine to ablate the thyroid after surgery (the ablation group, A) and monoexpotential for these receiving subsequent treatments for residual or recurrent disease (the follow up group, FU). The faster clearance in the follow-up patients generally resulted in less stringent restrictions than those advised for ablation patients. The rapid clearance of radioiodine in patients treated on one or more than one occasion means that therapy could be administered at home to selected patients with suitable domestic circumstances. In most cases the restriction times, despite the high administered activities, are less than those for patients treated for thyrotoxicosis. The concentration of radioiodide in domestic drainage systems should not pose a significant risk