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.
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