What determines whether radioactive iodine treatment might be effective?

Differentiated thyroid cancer cells may undergo a process of transformation whereby they lose some or all of the ability to take up and retain 131-Iodine. In order to determine whether or not administration of radioactive iodine may be an effective treatment for recurrent thyroid cancer, it is necessary to determine whether or not any thyroid cancer cells that have been detected still have the ability to take up 131-Iodine. This is most readily accomplished by performing a radioactive iodine scan. If a whole-body scan shows evidence of abnormal uptake in areas where thyroid cancer cells are known to be present, those cells are considered to be iodine avid. As such, they may be effectively treated with administration of higher doses of 131-Iodine. If a whole-body scan does not show any evidence of uptake in regions where thyroid cancer cells are known to be present, they are considered to be non-avid. This situation presents something of a dilemma, as in most circumstances it is not clear whether further treatment with 131-Iodine would help in any way. Some experts advocate proceeding with treatment when an elevated thyroglobulin level has been confirmed. In such cases, a decrease in the thyroglobulin level may be considered to represent a response to treatment.

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