To Ablate or Not to Ablate: Issues and Evidence Involved in 131I Ablation of Residual Thyroid Tissue in Patients with Differentiated Thyroid Carcinoma

Ablation of residual thyroid tissue after total or near-total thyroidectomy is widely accepted by many practitioners and endorsed by relevant professional societies in the United States and the international community for patients with defined risk factors, including age greater than 45 years, large tumors; tumors with undesirable histopathology; lymph node involvement; positive surgical margins; gross and possibly microscopic extrathyroidal extension; and, of course, evidence or suspicion of distal metastases, including mediastinal lymphadenopathy, pulmonary or osseous metastases or involvement of other organs. 131I therapy doses of 3.7-5.5 GBq (100-150 mCi) should be used, and additional activity should be used in the event there are additional findings on pretreatment whole-body scans. Depending upon the patient's age, general medical condition, and renal function, nuclear medicine practitioners should be prepared to perform whole body (blood or bone marrow) dosimetry in the event doses >5.5 GBq (150 mCi) are being considered to assure patient safety. Still unresolved is the role of 131I ablation in the so-called “low risk” patient—particularly in a patient who has undergone a near-total thyroidectomy in the hands of a skilled surgeon. If an ablative dose is to be administered, 0.9-1.8 MBq (25-50 mCi) appears to be sufficient to eliminate most if not all thyroid tissue. The problem is defining the “low-risk” patient. After review of the extensive literature on this subject, it appears that the thoughtful and informed practitioner must make a patient specific decision in this setting on the basis of his/her experience and review of the details in each case and continue to review the evidence on this subject as it becomes available.