After the first radioactive iodine (RAI) treatment, if a whole-body scan shows a reduction in the size or number of metastatic lymph nodes or a decrease in Tg levels, the cancer is able to take up iodine and the treatment is effective. However, thyroglobulin (Tg) levels may not drop to the desired level (usually below 1.0 ng/ml) after a single treatment, so a second or more treatments may be considered, with an interval of 4-6 months between treatments until Tg levels reach the standard. Thyroxine tablets may be taken during the interval.
The dose of iodine-131 (I-131) used for the first RAI treatment is usually 100 to 150 mcuries. If this dose is not effectively controlled, or if the Tg does not fall to a satisfactory level, the cancer tissue is “radioiodine resistant” and RAI therapy is not working. The doctor may consider other treatment strategies. In this case, if the tumor grows slowly and the patient’s overall condition is stable, follow-up can be maintained with adequate communication with the doctor. If the review reveals an increase in the number of metastatic lymph nodes and a rapid growth rate, the doctor will take appropriate measures, such as trying targeted drug therapy or reoperation.
Co-written by Dr. Kai Guo, Cancer Hospital of Fudan University