Radioactive Iodine Treatment

The thyroid uses iodine as its main raw material and so this radioactive form concentrates in the colloid (hormone forming) tissue in the thyroid gland.

I 131 concentrates in the cells and its radioactivity destroys them.  Depending on how much is given initially depends of course on the severity of cellular damage.  The amount given is calculated by body weight and the presumed severity of the over-activity of the thyroid forming cells.

There are three possible scenarios.  One is that the calculation was right.  The amount of thyroid tissue left is just right to produce the right level of hormones in the bloodstream.  Of course, the cells may later partly recover, and then it may have to be done all over again or further damage and loss of function may occur and the thyroid as a whole may become underactive.

The second scenario is that the patient continues to have an overactive thyroid in spite of treatment, and a further dose of radioactive iodine – or doses – may have to be given at once.

The third scenario is a good deal more common.  Overkill becomes evident in a few days, and thyroid hormone in the bloodstream falls pretty quickly.  Very soon thyroid replacement (usually thyroxine) becomes necessary.