Thyroid Research Thyroid Research Archive Thyroid Cancer

Low and moderate doses of radioiodine are equally effective for ablation of thyroid remnants in patients with thyroid carcinoma

(July 2004)

The background of the study. Most patients with papillary or follicular thyroid carcinoma are treated with iodine (I)-131 after surgery to destroy any remaining normal thyroid tissue. The optimal dose for this purpose is not known. This study was a randomized trial of the efficacy of different doses of I-131 for thyroid-remnant ablation.

How the study was done. Five hundred nine patients with thyroid carcinoma were randomly assigned to receive 15 to 50 mCi (555 to 1850 MBq) of I-131 in increments of 5 mCi (185 MBq). The ratio of females to males was 2.6 to 1. Tumor size averaged 5 cm. Six months after treatment, the patients underwent a whole-body scan 48 hours after administration of 2 to 3 mCi (74 to 111 MBq) of I-131. Ablation was considered successful if any two of the following criteria were met: the scan was negative, 48-hour I-131 uptake was ≤0.2 percent, and serum thyroglobulin was ≤10 ng/ml. Patients in whom ablation was not successful were given another dose of I-131.

The results of the study. The clinical characteristics, tumor type and size, and I-131 uptake at the time of treatment were similar in the patients in all eight treatment groups. The I-131 treatment was successful in 395 patients (78 percent) overall. The success rate was approximately 60 percent in the patients who received 15 and 20 mCi (555 and 740 MBq), and approximately 80 percent in those who received the higher doses. Factors associated with successful ablation were more extensive thyroidectomy, lower initial I-131 uptake, and I-131 dose ≥25 mCi (925 MBq).

The conclusions of the study. In patients with thyroid carcinoma, I-131 doses ranging from 25 to 50 mCi (925 to 1850 MBq) are equally effective in destroying the thyroid remnant.

The original article. Bal CS, Kumar A, Pant GS. Radioiodine dose for remnant ablation in differentiated thyroid carcinoma: a randomized clinical trial in 509 patients. J Clin Endocrinol Metab 2004;89:1666-73.