Outcome of Radioactive Iodine Ablation/Treatment in Pathologically-Defined Low Risk of Recurrence Well-Differentiated Thyroid Carcinoma Patients

Abstract

Objective: To evaluate outcome of radioactive iodine (RAI) ablation/treatment in pathologically defined low risk of recurrence well-differentiated thyroid carcinoma (WDCT) patients.
Methods: A 7-year retrospective review of medical records was done in 155 pathologically defined low risk of recurrence (LRR) WDTC patients. Total thyroidectomy or equal surgery and pre-ablative evaluation were done in all patients. The 1^st dose of RAI ablation was either 30 or 80/100 mCi. The following doses of RAI ablation/treatment were adjusted by patients’ risk of recurrence and treatment response. Criteria of successful ablation/treatment were 1) no evidence of clinical disease 2) no demonstrable abnormal uptake on the follow up 6-12 months diagnostic whole body scan (Dx-WBS) and 3) stimulated thyroglobulin (Tg) lower than 2 ng/mL and thyroglobulin antibodies (TgAb) lower than 40 IU/mL. Patients received RAI ablation/treatment until they achieved disease remission or there was evidence of treatment failure.
Results: Cumulative success rate after the 1^st, 2^nd and 3^rd RAI ablation/treatments were 61.3%, 75.5% and 82.6%, respectively. The risk of recurrence among 155 patients were 83.2% low risk (n=129), 11.6% intermediate risk (n=18), and 5.2% high risk (n=8). Of 129 true LRR patients, the success rates of 1^st, 2^nd and 3^rd RAI ablation were 73.6% (n=95), 10.1% (n=13) and 6.2% (n=8), respectively. After RAI treatment for 3 sessions, disease remission was observed in 10 of 18 intermediate risk of recurrence (IRR) patients and only 1 of 8 high-risk of recurrence (HRR) patients. Between success and failure group, there was statistically significant difference in risk of recurrence (p-value = 0.000), baseline Tg (2.61 vs 7.17 ng/mL, p-value = 0.015) and TgAb (16.8 vs 33.7 IU/mL, p-value = 0.004).
Conclusion: Disease remission in pathologically defined LRR patients after the 1^st, 2^nd and 3^rd sessions of RAI ablation/treatment were 61.3%, 75.5% and 82.6%, respectively. IRR and HRR were found in 16.8% of pathologically defined LRR patients. Risk of recurrence, baseline Tg and TgAb strongly correlated with RAI ablation/treatment outcome. Highest success rate was observed in true LRR (89.9%). None of the IRR and HRR patients had disease remission following the 1^st RAI ablation and remission rate was only 43.2% following 3 sessions of RAI treatment.