Background:
The purpose of this study was to evaluate the utility of surveillance with annual whole-body iodine-131 (131i) scintigraphy for patients with recurrent thyroid carcinoma.
Methods:
The records of patients with thyroid carcinoma were reviewed. the 76 patients included in this study had undergone thyroidectomy and postoperative 131i therapy, and had at least 1 negative whole-body 131i scintigraphy 1 year after 131i therapy. there were 59 females and 17 males (age range, 12-74 years). surgery consisted of a total thyroidectomy for 84% of patients and a subtotal thyroidectomy for 16%. 131i was administered within 1 month of thyroidectomy and annually thereafter until complete ablation of remaining thyroid tissue occurred. annual follow-up diagnostic whole-body 131i scintigraphy was performed at years 1 and 2, and then every 3-5 years. some patients also had scintigraphy performed in years 3, 4, and 5.
Results:
Patients received 1-4 annual administrations of 131i (median, 1). the administered activity per treatment was 30-211 mci, and the total activity administered that was necessary to achieve complete ablation of functioning thyroid tissue ranged from 30 to 514 mci (median, 100 mci). the relapse free survival at both 5 and 10 years was 88%. by definition, all of these patients had a negative 131i scintigraphy at 1 year after their last therapeutic 131i administration. seven patients had a positive 131i scintigraphy 1 year after the first negative scintigraphy. two other patients had positive 131i images after 2 consecutive negative annual 131i scintigraphic studies. the predictive value for relapse free survival of 1 negative diagnostic 131i study of these patients was 91% (+/- 0.02), and for 2 consecutive annual negative 131i studies the value was 97% (+/- 0.02); these results were significantly different (p = 0.0197). a stepwise logistic regression analysis was performed in an effort to identify risk factors for disease recurrence after complete ablation. none of the variables assessed--age, gender, tumor histology, tumor size, vascular invasion, capsular invasion, surgical margin status, or lymph node status--was predictive of recurrence after complete ablation.
Conclusions:
A single negative 131i scintigraphic study after complete ablation has a lower predictive value for relapse free survival than do two consecutive annual negative studies. annual 131i imaging is recommended for surveillance until 2 consecutive annual negative studies are obtained, after which repeat imaging at 3-5 years appears to be satisfactory.