RESUMEN
Aim of the study: to determine the efficacy of a 100mCi dose for ablation of thyroid remnants; the influence of pre-therapy 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 %wer e 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 [46] or ectopic [216] 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