Role Of Radioactive Iodine Therapy

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Radioactive iodine (131I) therapy is well accepted as an adjunct to surgery for both ablation of postoperative thyroid remnants and treatment of metastatic

Figure 2-12. Radiograph of the neck and upper chest of a patient following injection of iodized oil (Lipiodol) into the thyroid gland. Note the flow of contrast laterally and downward along lymphatic channels. Courtesy of O. H. Clark, MD, Department of Surgery, University of California-San Francisco/Mount Zion Medical Center, San Francisco, CA.

Figure 2-12. Radiograph of the neck and upper chest of a patient following injection of iodized oil (Lipiodol) into the thyroid gland. Note the flow of contrast laterally and downward along lymphatic channels. Courtesy of O. H. Clark, MD, Department of Surgery, University of California-San Francisco/Mount Zion Medical Center, San Francisco, CA.

disease. However, there is much debate on the selection of patients for postoperative 131I remnant ablation among those who have undergone "potentially curative" surgery because radioiodine therapy may not alter the course of the disease in patients in the low-risk category. Nevertheless, postoperative remnant ablation affords the theoretical advantage to (1) destroy occult microscopic carcinoma cells within the thyroid remnant, (2) facilitate radioiodine scanning by the destruction of remaining normal thyroid tissue, and (3) improve the value of serum Tg measurements during follow-up.20

Among our series of patients with DTC with primary tumor > 1 cm in size, we found a twofold higher risk of tumor recurrence in the cohort who did not have postoperative adjuvant 131I ablative therapy (Figure 2-13).15 Most experts agree that the improved disease-free survival associated with 131I remnant ablation provides sufficient ground to recommend 131I ablation of residual thyroid tissue in most DTC patients who have undergone total or near-total thyroidectomy.1719 This is not indicated, however, in very low-risk category patients who are treated with lobectomy.

On the other hand, the role of adjuvant radioio-dine therapy for patients with persistent or recurrent neck disease or distant metastatic lesions is less controversial (Figure 2-14). This is especially effective if the tumor is occult or microscopic and involves larger administered doses of 131I, which necessitates

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Figure 2-13. Disease-free survival in patients with differentiated thyroid carcinoma in whom the primary tumor size is > 1 cm, comparing the groups with and without postoperative radioactive iodine (131I) ablation (p < .0001 between treatment groups). Reproduced with permission from Loh KC et al.15

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Figure 2-13. Disease-free survival in patients with differentiated thyroid carcinoma in whom the primary tumor size is > 1 cm, comparing the groups with and without postoperative radioactive iodine (131I) ablation (p < .0001 between treatment groups). Reproduced with permission from Loh KC et al.15

Figure 2-14. Total-body scan performed 72 hours after high-dose (200 mCi) radioactive iodine (131I) therapy in a previously treated papillary thyroid carcinoma patient who developed nodal recurrence. Note the increased 131I uptake in the right submandibular (thick arrow) and supraclavicular (thin arrow) regions, respectively. Courtesy of E. S. Ang, MD, Department of Nuclear Medicine, Singapore General Hospital, Singapore.

Figure 2-14. Total-body scan performed 72 hours after high-dose (200 mCi) radioactive iodine (131I) therapy in a previously treated papillary thyroid carcinoma patient who developed nodal recurrence. Note the increased 131I uptake in the right submandibular (thick arrow) and supraclavicular (thin arrow) regions, respectively. Courtesy of E. S. Ang, MD, Department of Nuclear Medicine, Singapore General Hospital, Singapore.

radiation isolation either in the hospital or at home. After total thyroidectomy, treatment with a therapeutic dose of 131I (approximately 100 to 200 mCi) was associated with successful ablation of micrometas-tases in the lung in about 70% of patients, whereas when pulmonary metastases were identified on chest radiographs, curative 131I ablation was achieved in only about 10% of patients (Figure 2-15). Microscopic bone metastases identified with 131I total-

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