Relationship between TSH Level and Effective Half-life of I-131 in Differentiated Thyroid Cancer Patients

Abstract

The retained activity and Effective half life at 24h of therapeutic 131I in patients with Differentiated Thyroid Cancer (DTC) after total and non-total (sub-total, near-total, partial thyroidectomy and lobectomy) thyroidectomy were compared for patients in these 2 surgical groups. A total of 82 patients (61 females and 21 males) mean age 37.2 ± 9.3 years, mean weight 70 ± 15.6 Kg were considered in this study. 58 patients (70.73%) had papillary Cancer and 24 (29.27%) had follicular cancer. Out of 82 patients, 37 had total thyroidectomy while 45 had non total thyroidectomy (sub-total-29, near total- 10, partial thyroidectomy-4 and lobectomy- 2). 6 patients (7.3%) had metastases. The retained 131I activity (as a percentage of the administered dose in MBq) was 4.61% - 44.56% for patients with total thyroidectomy (mean-26.91 ± 12.57%) compared to 10.18% - 55.36% for patients with non-total thyroidectomy (mean-32.41 ± 12.57%). (p < 0.05) The effective half life ranged between 0.20 – 0.86 days for patients with total thyroidectomy (mean- 0.51 ± 0.21 days) and 0.20 – 1.17 days for patients with non-total thyroidectomy (mean- 0.62 ± 0.27 days). There is no significant difference in the mean effective half lives for the two groups of patients (p = 0.032). Our data suggests that exposure to radiation after ingestion of 131I is similar in both groups studied.