Summary
Aim: To compare the success rates of radioiodine therapy (RIT) for thyroid remnant ablation (TRA) after the administration of a high-standard activity (3700 MBq; 100 mCi) to a lower-activity regimen of 2000 MBq (54 mCi) I-131 in a cohort of differentiated thyroid carcinoma (DTC) patients (papillary, follicular, mixed, pT1a(m) – pT3, N0 – NX, R0). Methods: 135 patients received approx. 2000 MBq I-131 (54 mCi) for thyroid remnant ablation after total thyroidectomy for DTC, 137 patients received approx. 3700 MBq (100 mCi) I-131. Ablation success was defined as thyroglobulin (TG) levels < 0.5 ng/ml after stimulation, negative I-131 whole-body scan and inconspicuous results on neck ultrasonography approximately 6 months after initial RIT. Results: In the follow-up 84.4 % of patients in the reduced-activity group and 87.6 % of the patients in the standard-activity group did not show any relevant residual I-131 uptake in the thyroid bed (p = 0.454). 90 % in the reduced-activity group and 91 % in the standard-activity group demonstrated a stimulated TG level < 0.5 ng/ml (p = 0.969). All patients were unre-markable in cervical ultrasonography. The success rate was comparable in both groups (81.5 % in the reduced-activity group vs. 83.9 % in the standard-activity group, p = 0.592). No re-therapy was required in 85.2 % of the patients in the low-activity group as compared to 87.6 % of the patients in the standard-activity group (p = 0.563). Conclusions: We could demonstrate that irrespective of the activity administered, the patients had comparable success rates with regard to TRA as defined by our criteria. We thus consider the use of a reduced-activity regimen for TRA safe and feasible in the patient cohort examined in this study.
Predictivity of stimulated serum thyroglobulin and antithyroglobulin antibodies for the efficacy of thyroid remnant ablation on patients with differentiated
thyroid carcinoma