Comparison of Radioactive Iodine Activities in Terms of Short- and Long-term Results in Ablation Therapy in Patients with Low-risk Differentiated Thyroid Cancer.

Abstract

The aim of this study was to compare the treatment responses after ablation with 30-50 mCi radioactive iodine (RAI) and 100 mCi RAI in patients with differentiated thyroid cancer (DTC) who were in the low-risk group according to 2015 American Thyroid Associations Classification (ATA 2015) criteria. Between February 2016 and August 2018, 100 patients who received RAI treatment in our clinic after total thyroidectomy and who were in the low-risk group DTC were included in this retrospective study. These patients were divided into 2 groups: low-activity (30-50 mCi) (group 1) and high-activity (100 mCi) (group 2). While 54 patients were treated with low activity, 46 patients received high activity RAI. The 2 groups were compared according to the 1st- and 3rd-year treatment response status. According to the first-year follow-up, 15 patients were accepted as indeterminate response and 85 patients as excellent response. Three (5.5%) of the patients who were accepted as indeterminate response were in group 1 and 12 (26%) were in group 2. According to the third year follow-up, 1 patient in group 1 and 3 patients in group 2 were accepted as indeterminate response. No biochemical incomplete response or recurrent disease was detected. In the chi-square analysis performed to investigate the relationship between the first-year treatment response and RAI activities, a significant relationship was found (p=0.004). In the Mann-Whitney U test performed to investigate the parameters that may be effective in the treatment response, only the preablative serum thyroglobulin value was shown to have a significant difference between the two groups (p=0.01). In the long-term follow-up of the patients, based on the third year treatment response data, chi-square analysis was performed to evaluate the two groups in terms of treatment responses, and no statistically significant relationship was found (p=0.73). Ablation with 30-50 mCi can be safely applied in DTC patients who are in the ATA 2015 low-risk group and are planned for RAI ablation treatment.