Comparison of treatment efficacy 1 and 2 years after thyroid remnant ablation with 1110 versus 5550 MBq of iodine-131 in patients with intermediate-risk differentiated thyroid cancer.

BACKGROUND: Radioiodine ablation may be associated with improved survival in patients with intermediate-risk follicular cell differentiated thyroid cancer (FCDTC). The aim of this study was to compare ablation efficacy of 1110 versus 5500 MBq of iodine-131 (I) in FCDTC patients with intermediate risk. METHODS: Thirty-nine patients with intermediate-risk FCDTC (T3N0, T1-2N1b and T1-3N1a) were treated with 1110 MBq of I and compared with 43 age-matched and sex-matched patients who received 5550 MBq of I. Patients with invasive histology, extensive lymph node involvement, and preablation thyroglobulin (Tg) of more than 100 ng/ml were excluded from the study. All patients underwent total or near total thyroidectomy with or without lymph node dissection. Response to treatment was evaluated 1 and 2 years after I treatment. RESULTS: We studied four male and 78 female patients, age range 21-69 years. Preablation Tg level was 12.7±17.8 and 15.8±22.6 ng/ml in patients in the low-dose and high-dose groups, respectively (P=0.48). Anti-Tg antibody level as well as T and N staging were not significantly different in the two groups (P>0.2). One and 2 years after treatment, an excellent response was noted in 19 and 22 patients in the low-dose group and in 16 and 23 patients in the high-dose group, respectively (P>0.3). Using logistic regression analysis, preablation Tg was the only significant factor in the prediction of an incomplete response 2 years after therapy. CONCLUSION: 1110 MBq of I was as effective as 5550 MBq of I in the treatment of FCDTC patients with intermediate risk 1 and 2 years after therapy.