Success Rate of Radioactive Iodine Ablation in Low-Risk of Recurrence Well-Differentiated Thyroid Carcinoma Patients

Abstract

Objective: To evaluate success rate and factors affecting the success of radioactive iodine (RAI) ablation in low-risk of recurrence well-differentiated thyroid carcinoma patients.
Methods: Retrospective review of medical records was done in 132 low-risk of recurrence well-differentiated thyroid cancer (WDTC) patients between January 2007 and December 2013. All patients underwent 1) total thyroidectomy or equal surgery and 2) pre-ablative evaluationwith ^99mTc-pertechnetate thyroid scan and 24-hour ¹³¹I thyroid uptake. RAIablation using low activity (30 mCi: n = 17) or high activity (80 or 100 mCi: n = 115) were given. Success rate of each activity and a comparison of success rates between 2 doses were analyzed. Criteria of successful ablation were composed of 1) no palpable neck mass 2) no demonstrable thyroid and tumor uptake on the follow up 6-12 months diagnostic whole body scan (WBS) and 3) stimulated thyroglobulin (Tg) lower than 2 ng/mL in the absence of interfering thyroglobulin antibodies (TgAb <40 IU/mL). Factors that may affect success of radioactive iodine ablation were studied; age, gender, tumor size, stage, pathological result, number of lesions, pre-ablation  24-hour ¹³¹I thyroid uptake, serum T4, TSH, Tg and TgAb at time of ablation. 

Results: Overall success rate of RAI ablation was achieved in 95 patients out of 132 patients (72%). Low and high dose RAI ablation were completed in 9/17 patients (52.9%) and in 86/115 patients (74.8%), respectively (p-value = 0.082). Baseline Tg at time of ablation was a factor related to the success of ablation. Median Tg in success and failure group was 2.61 and 7.18 ng/mL, respectively (p = 0.023).
Conclusion: Success of ¹³¹I ablation in low-risk of recurrence well-differentiated thyroid cancer patients was 72%. The factor relating to ablative success was Tg level at time of ablation.