Metastatic Thyroid Carcinoma

The purpose of this study is to evaluate a new diagnostic imaging test, positron emission tomography (PET), with a different radioactive form of iodine called iodine-124. This form is able to accurately measure the amount of radioactive iodine uptake in the cancer. If the new test determines sufficient radioiodine uptake in the cancer, treatment will continue as usual. However, if the new test shows only low radioiodine uptake, a decision may be made that the benefit from radioiodine therapy is insufficient and that another form of therapy is preferred.