SodiumIodide[131I]

Diagnostic use of sodium iodide(¹³¹I) with microcurie doses for evaluating thyroid functionand/or morphology is no longer preferred because ofthe higher radiation dose associated with particle decayfrom this isotope. Doses from 1 to 10 mCi (37–370 MBq)are used for whole-body imaging to detect metastatic thyroidcancer and/or residual thyroid tissue following thyroidectomy.Whole-body images are obtained 48 to 72hours later.
Therapeutic use of sodium iodide (¹³¹I) occurs in hyperthyroidismor differentiated types of thyroid cancers. A patientwith hyperthyroidism will receive an oral dose of 5 to10 mCi (185–370 MBq) of sodium iodide (¹³¹I). The dosecould be higher for patients with toxic nodular goiter orother special situations. Treatment doses for differentiatedthyroid carcinoma with or without metastases range from 30to 200 mCi (1,110–7,400 MBq). Seven days after the therapeuticdose, a whole-body scan is performed in an effort todetect metastases not seen on the pretherapy diagnostic images.Thyroid hormone medication will be discontinued forseveral weeks prior to radiotherapy and thyroid-stimulatinghormone (TSH) levels must be evaluated to ensure maximaluptake of the radiotracer for therapy.