Treatment rationale in thyroid carcinoma. Effect of scan dose.

The authors have previously shown that the definition of ablation of thyroid tissue in patients treated with thyroidectomy and radioiodine (I-131) for thyroid carcinoma depends upon the dose of I-131 used to scan the patient. The therapeutic response to I-131 therapy was evaluated in a group of ten differentiated thyroid cancer patients who had a negative 2-mCi (-2 mCi) diagnostic study, but had a positive 10-mCi (+10 mCi) diagnostic study (group 1) during their follow-up evaluation. These results were compared to another group of ten differentiated thyroid cancer patients who received I-131 ablation therapy based on a positive 2-mCi (+2 mCi) I-131 scan (group 2). Six patients in group 1 and eight in group 2 had improvement or ablation of residual tissue based on the 10-mCi scan following therapy. The difference in response between the two groups was not statistically significant (P = 0.63) by two-tailed Fisher's exact test, indicating that even patients with -2-mCi, but +10-mCi scans may respond to I-131 therapy. Whether the large dose therapy makes any impact on the clinical outcome has not been answered by this study.