doi:10.1016/j.ijrobp.2004.01.036 CLINICAL INVESTIGATION Head and Neck EFFICACY OF I 131 ABLATION THERAPY USING DIFFERENT DOSES AS DETERMINED BY POSTOPERATIVE THYROID SCAN UPTAKE IN PATIENTS WITH DIFFERENTIATED THYROID CANCER JAMAL ZIDAN, M.D.,* † ELIOZ HEFER, M.D., ‡ GALINA IOSILEVSKI,PH.D., § KAREN DRUMEA, M.D., ‡ MOSHE E. STEIN, M.D., ‡ ABRAHAM KUTEN, M.D., †‡ AND ORA ISRAEL, M.D. †§ *Oncology Unit, Sieff Government Hospital, Safed; † Faculty of Medicine, Technion, Israel Institute of Technology; ‡ Department of Oncology, Rambam Medical Center; § Institute of Nuclear Medicine, Rambam Medical Center, Haifa, Israel 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 >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 . © 2004 Elsevier Inc. Differentiated thyroid cancer, Postoperative treatment, I 131 ablation, Optimal dose. INTRODUCTION Surgical resection to achieve local disease control re- mains the cornerstone of primary treatment for most thyroid cancers. Ablation of residual thyroid tissue by oral administration of I 131 after surgery is considered standard management for most patients with differenti- ated thyroid carcinoma (1–3).I 131 ablation of remnant thyroid tissue in patients with papillary and follicular carcinoma who have undergone total or subtotal thyroid- ectomy is important in the detection of metastatic disease and the destruction of the remaining thyroid tissue with residual microscopic cancer (4). Normal thyroid tissue takes up I 131 more avidly than does cancer and thus prevents full visualization of the true disease extent (5). Another important advantage is that I 131 ablation re- moves the contribution of normal thyroid tissue serum thyroglobulin, an important tumor marker in the fol- low-up of postoperative patients (6). Despite the obser- vation of Cady and Rossi (7) that no survival enhance- ment was documented with the use of I 131 for ablation, many studies have reported that I 131 ablation decreases cancer death, tumor recurrence, and the development of distant metastases (7–10). There is no fixed policy on the dosage of radioiodine needed to ablate remnant thyroid tissue effectively. Some physicians prefer low doses of around 30 mCi, and others argue for doses as high as 200 mCi. A success rate of 50 –90% has been reported with different doses (11–13). Successful ablation has been reported with a single initial administration of I 131 when the treatment was standard- ized to a radiation dose of 300 Gy in the residual thyroid (14, 15). The aim of this study was to evaluate the optimal dose of I 131 for remnant tissue ablation in patients with dif- ferentiated thyroid cancer after total and subtotal thyroid- ectomy using a variable administered dose schedule on the basis of the percentage of I 131 uptake postoperatively through a prospective clinical trial. Reprint requests to: Jamal Zidan, M.D., Oncology Unit, Sieff Government Hospital, P.O. Box 1008, Safed 13100, Israel. Tel: (+972) 4-682-8550; Fax: (+972) 4-682-8621; E-mail: zidan.j@ ziv.health.gov.il Received Mar 27, 2003, and in revised form Jan 20, 2004. Accepted for publication Jan 23, 2004. Int. J. Radiation Oncology Biol. Phys., Vol. 59, No. 5, pp. 1330 –1336, 2004 Copyright © 2004 Elsevier Inc. Printed in the USA. All rights reserved 0360-3016/04/$–see front matter 1330