THE EFFECTS OF RADIOACTIVE IODINE IN THYROID REMNANT ABLATION AND TREATMENT OF WELL-DIFFERENTIATED THYROID-CARCINOMA

Although the use of radioactive iodine (I-131) in the treatment of thy roid cancer is well established, treatment dose is not well standardiz ed. In order to deduce the appropriate dose for thyroid remnant ablati on and the effect of I-131 in the treatment of distant metastases, dat a for 544 patients with papillary or follicular thyroid cancer were re trospectively reviewed. All patients received surgical treatment follo wed by post-operative I-131. If remnants were present in the 0.2 GBq I -131 diagnostic scan, 1.1-3.7 GBq I-131 were administered for ablation . For the treatment of distant metastases 3.7-5.6 GBq were used. Of 31 8 patients receiving I-131 for thyroid remnant ablation, 290 were succ essfully ablated. After one dose of 1.1 GBq I-131, 82% (159/194) of th yroid remnants were ablated. During the follow-up period, two of 14 St age IV patients with lung or mediastinal metastases at the time of ope ration achieved complete clinical remission. Factors identified as inf luencing response to I-131 therapy included age, clinical stage, survi val, recurrence, extent of surgery and the 1 month post-operative seru m thyroglobulin (Tg) level. In conclusion 1.1 GBq I-131 was adequate f or thyroid remnant ablation unless distant metastases were present. Ra dioactive I-131 has a role in the treatment of well differentiated thy roid carcinoma with pulmonary metastases but seems to be less effectiv e for treatment of bone metastases.