Outcome of Ablation of Thyroid Remnants with 100mCi (3.7GBq) Iodine-131 in Patients with Thyroid Cancer

Aim of the study: To determine the efficacy of a 100mCi dose for ablation of thyroid remnants; the influence of pretherapy scanning; correlation between cervical uptake and efficacy; and the necessity of diagnostic scan for the patients with low serum Tg in the follow-up after remnant ablation. Patients and Methods: A retrospective study was conducted on 98 patients with differentiated thyroid cancer without metastases who received an ablative dose of 100mCi (3.7GBq)of iodine-131 after total thyroidectomy. Results: Six months to one year after ablation, 81/98 patients (82.6%) had a negative scan. Diagnostic scanning with 5mCi (185MBq) performed 72h or 3 months before ablation did not interfere with treatment success compared to patients not submitted to pre-therapy scanning. Pre-ablation cervical uptake values 2% were associated with a higher ablation efficacy (92.8%), from 2 to 5% showed 79% success and values 5%, 57.1% (p 0.05). There were no significant differences between the responsive and non responsive groups in terms of age, sex, histological type or size of the primary tumor. 10.5% of the patients with low stimulated Tg ( 2ng/ml) presented discrete thyroid bed uptake on follow-up diagnostic scan ( 0.5%) without definitive residual disease and 79.4% had negative uptake on scan. The patients with Tg 2ng/ml presented thyroid bed (4/6) or ectopic (2/6) uptake on followup diagnostic scan. Conclusion: An ablative dose of 100mCi shows a high rate of efficacy, especially when cervical uptake is 2%; no difference was noted between patients assessed by scan within 72h or 3 months before treatment and those not scanned; follow-up diagnostic scan can be avoided in low risk patients with stimulated Tg 2ng/ml.