Why are further radioactive iodine scans necessary?

In some cases, even after extensive thyroid surgery and treatment with high doses of radioactive iodine, thyroid cancer may persist, recur, or metastasize to other parts of the body. In cases where thyroid cancer persists or recurs in the neck, it may grow so slowly that it is not immediately detectable on physical exam. In cases where thyroid cancer metastasizes to other parts of the body, it may spread and grow without producing any symptoms that raise suspicion. For these reasons, radioactive iodine scans are used to help monitor patients for persistence or recurrence of thyroid cancer over time. The selective uptake of radioactive iodine by thyroid cancer cells makes it possible to use scans that image a patient's whole body to detect and localize areas of thyroid cancer. These scans are an important means of determining whether thyroid cancer has been completely eradicated, or whether it may be necessary to proceed with further evaluation and treatment. They may be critical in cases where persistent or recurrent thyroid cancer cannot be detected with blood tests.

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