The effects of radioactive iodine in thyroid remnant ablation and treatment of well differentiated thyroid carcinoma.

Although the use of radioactive iodine (131I) in the treatment of thyroid cancer is well established, treatment dose is not well standardized. In order to deduce the appropriate dose for thyroid remnant ablation and the effect of 131I in the treatment of distant metastases, data for 544 patients with papillary or follicular thyroid cancer were retrospectively reviewed. All patients received surgical treatment followed by post-operative 131I. If remnants were present in the 0.2 GBq 131I diagnostic scan, 1.1-3.7 GBq 131I were administered for ablation. For the treatment of distant metastases 3.7-5.6 GBq were used. Of 318 patients receiving 131I for thyroid remnant ablation, 290 were successfully ablated. After one dose of 1.1 GBq 131I, 82% (159/194) of thyroid remnants were ablated. During the follow-up period, two of 14 Stage IV patients with lung or mediastinal metastases at the time of operation achieved complete clinical remission. Factors identified as influencing response to 131I therapy included age, clinical stage, survival, recurrence, extent of surgery and the 1 month post-operative serum thyroglobulin (Tg) level. In conclusion 1.1 GBq 131I was adequate for thyroid remnant ablation unless distant metastases were present. Radioactive 131I has a role in the treatment of well differentiated thyroid carcinoma with pulmonary metastases but seems to be less effective for treatment of bone metastases.