Success Rate in Preparation of Patients with Thyroid Cancer for I-131 Total Body Scan by 3-Week Discontinuation of Thyroxine

Abstract

Objective: The purpose of this study was to evaluate the success rate in preparation of patients with thyroid cancer for I-131 total body scan by 3-week discontinuation of LT4 including clinical characteristics affecting the success.

Methods: Ninety-six patients with well-differentiated thyroid cancer on LT4 suppressive treatment were indicated for I-131 total body scan. After 3-weeks of LT4 withdrawal, T4 and TSH were measured whether TSH was ≥ 30 mIU/L. Then I-131 total body scan, Tg and TgAb measurements were performed upon achievement of TSH ≥ 30 mIU/L. If TSH was below 30 mIU/L, LT4 was still withheld and T4 together with TSH were evaluated weekly until TSH was ≥ 30 mIU/L. The percentage of success rate after 3-week withdrawal of LT4 was studied. Clinical characteristics between the success and failure rates after LT4 withdrawal for 3 weeks were compared.

Results: Success rate in preparation for I-131 total body scan was 54.2%, 81.3% and 93.8% by discontinuation of LT4 for 3, 4 and 5 weeks, respectively. Bivariate analysis indicated that factors which significantly affected the success were age (pvalue = 0.0002), baseline TSH (p-value = 0.041) and cancer staging (p-value = 0.019). When multivariate analysis was used, only age and staging affected the success, independently. Patients who were older than 45 years old and stage I together with patients who were older than 45 years old and above stage I had more tendency to not achieve the target TSH after 3-week LT4 withdrawal as compared to the patients who were younger than 45 years old and stage I (Odd ratio, 9.281; 95% C.I., 2.269-37.957 and Odd ratio, 8.25; 95% C.I., 2.793- 24.366, respectively).

Conclusion: The success rate of 3-week discontinuation of LT4 was 54.2%. This method should be considered in patients under the age of 45 years old or being classified as stage I.