What is a pre-treatment scan?

The radioactive isotope used to treat thyroid cancer actually releases two different types of energy as it undergoes decay. The first type of energy, called beta radiation, only travels a very short distance through tissues in the body, but is powerful enough to disrupt the normal functions of thyroid cancer cells. The second type of energy, called gamma radiation, travels farther when released. A special camera detects this gamma radiation to create a picture of the body that reveals where the 131-Iodine has been taken up and concentrated. This picture is called a radioactive iodine scan.

In treating thyroid cancer, radioactive iodine scans performed with small doses of 131-Iodine may be used for different purposes. Following thyroid surgery, a scan may be performed to see whether there is any tissue remaining in the neck that will take up 131-Iodine. This may help determine whether treatment with a much larger dose of 131-Iodine is necessary. A pre-treatment scan may also reveal areas of uptake outside the region of the neck that are concerning for possible metastases of thyroid cancer. This may prompt further investigation with other radiographic studies, and may persuade physicians to consider using higher doses of 131-Iodine in planning radioactive iodine treatment.

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