Efficacy of I131 ablation therapy using different doses as determined by postoperative thyroid scan uptake in patients with differentiated thyroid cancer.

PURPOSE: The optimal dose of I(131) for ablation of functioning residual thyroid tissue after surgery is controversial. The current study was conducted to determine the optimal dose of I(131) for remnant postoperative ablation. A review of the literature is included.

METHODS AND MATERIALS: A total of 238 patients with papillary and follicular carcinoma were treated with I(131) for ablation of a postoperative thyroid remnant. The I(131) dose was based on the 24-h percentage of neck uptake in the postoperative thyroid scans. Patients with < 5% uptake received a median of 85 mCi; 6-10% uptake, a median of 80 mCi; 11-15% uptake, a median of 60 mCi; 16-20% uptake, a median of 50 mCi; and > or =21% uptake, a median of 30 mCi. The ablation results were compared with the prognostic factors.

RESULTS: Complete ablation was observed in 40 (92%) of 43 patients receiving 85 mCi, in 31 (94%) of 33 who received 80 mCi, in 39 (95%) of 41 who received 60 mCi, in 51 (93%) of 55 who received 50 mCi, in 37 (94%) of 39 who received 30 mCi, and in 18 (96%) of 19 who received 30 mCi. The overall successful ablation rate was 94% (95% confidence interval, 89-100%).

CONCLUSION: Our findings suggest that patients with differentiated thyroid cancer can be treated with doses of I(131) according to the percentage of neck uptake of postoperative total body scan, with high complete ablation rates, without exposing patients to higher dose levels of I(131).