Why do patients need to be on a low-iodine diet?

Radioactive iodine treatment is most effective when large amounts of 131-Iodine are taken up by thyroid cancer cells. If a substantial amount of natural iodine is present in the body when 131-Iodine is administered, it will compete with the 131-Iodine for entry into cells, and may block uptake, limiting the delivery of an effective dose of radioactive iodine. Adherence to a low-iodine diet prior to treatment can help to minimize this problem.

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