Radioiodine delivers tumoricidal radioactivity to thyroid tissue and is used after appropriate surgery or in selected recurrent and metastatic disease.
Relationship to surgery
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Radioiodine delivers radioactivity to both benign and malignant thyroid tissue.
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In thyroid cancer, total thyroidectomy and removal of gross neck disease allow residual microscopic disease or distant metastases to receive an optimal dose.
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Radioiodine is not an alternative to surgical resection when disease is resectable.
Preparation and post-treatment assessment
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High TSH levels are required to drive radioiodine effectively into cells.
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The required TSH elevation can be achieved by rendering the patient hypothyroid off thyroxine or by injecting recombinant TSH before radioiodine administration.
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An uptake scan after radioiodine shows areas of iodine uptake throughout the body and may reveal metastases missed on initial imaging.
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The uptake scan contributes to risk stratification after initial treatment.
Recurrence and loss of iodine avidity
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Radioiodine may be considered for recurrence; multiple doses can treat unresectable disease or distant metastases.
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Most differentiated thyroid cancers concentrate iodine, but iodine avidity may be lost with advancing age, particularly in multiply recurrent disease.
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Loss of iodine avidity is called radioiodine refractory disease. External beam radiotherapy may be considered in such cases, although this is uncommon.