Thyroid remnant ablation: questionable pursuit of an ill-defined goal

Ablative therapy with I-131 in 30-mCi doses, directed to postsurgical remnants in patients with differentiated thyroid cancer, reduced visible I-131 uptake to zero or nearly zero in 81% of patients but did not protect against tumor recurrence in six of 69 patients who were followed for 2-5 yr. Recurrences developed within 5-37 mo. Effectiveness of 30-mCi doses of I-131 in producing ablation did not correlate with I-131 uptake by the thyroid remnant, surgeon's estimate of remnant size, or delivered dose to the remnant in rads, calculated using reasonable assumptions. These findings emphasize the difficulty of dosimetric measurements and calculations. The value of postsurgical ablative therapy in diminishing morbidity and mortality in patients with differentiated thyroid cancer has not yet been firmly established, and until this is done we advocate a conservative, economical approach to thyroid ablation with 30-mCi treatment doses of I-131 and 1-mCi neck-scanning doses to check on effectiveness of therapy.