Problems and complications in treatment with radioiodine in patients with differentiated thyroid cancer

Full text: In the treatment of patients with differentiated thyroid cancer (DTC), for better prognosis it is important to ablate the residual thyroid tissue with radioiodine after thyroidectomy. We reviewed 174 patients with DTC (papillary and follicular) treated with radical surgery and radioiodine. All cases had an adequate hypothyroid state before scanning and hormonal determination: FT4, TSH and Tg. Therapeutic doses of iodine ranged from 3.7 to 7.4 GBq. Annual reviews were done including hormones estimation and iodine scintigraphy. We observed that 2% patients did not have any residual thyroid tissue and hence there was no need of iodine ablation. 60 patients showing small residual thyroid tissue were given 3.7 GBq of iodine-131 as therapeutic dose. All responded well showing negative iodine scans with 185 MBq 131I and Tg levels becoming undetectable on follow up. 5/16 Patients with large residual tissue were re-operated and became negative on scan after a single therapy. However, from remaining patients with large residual tissue, six were treated with two ablative doses and in the others five, three doses were needed. Fourteen of the 20 patients having lymph nodes involvement required two or more doses. In patients with pulmonary metastasis a repeated doses of radioiodine was necessary. In 11 of 16 cases, a complete remission was observed on scanning and all of them had a undetectable Tg. In the remaining five, a tumoral activity persisted on scintigraphy and elevated Tg (8000 ng/ml as maximum value). Patients with bone metastasis also required high therapeutic doses of radioiodine (7.4 GBq). In our series, of eight patients (50%) showed successful ablation. In conclusion, (i) ablation of thyroid remnant with a sole radioiodine doses is related to the presence of functioning thyroid tissue and its minimum size (ii) attention should be paid to non pathological uptakes of radioiodine (iii) metastasis diagnosis of patients with DTC requires high and repeated doses of radioiodine (iv) DTC patients with normal 131I scanning and Tg elevated must be treated. (author)