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Comparison of Outcomes After ¹²³I Versus ¹³¹I Preablation Imaging Before Radioiodine Ablation in Differentiated Thyroid Carcinoma

Division of Nuclear Medicine, Department of Radiology, and Division of Hematology/Oncology, Department of Medicine, University of Cincinnati Medical Center, Cincinnati, Ohio

Correspondence: For correspondence or reprints contact: Edward B. Silberstein, MD, Division of Nuclear Medicine, G026 Mont Reid Pavilion, University Hospital, 234 Goodman St., Cincinnati, OH 45219. E-mail: silbereb{at}healthall.com

Detection of residual tissue after thyroidectomy for papillary or follicular thyroid carcinoma may be performed using diagnostic imaging with either ¹²³I or ¹³¹I. The former is often preferred to avoid "stunning"—defined as a reduction in uptake of the therapeutic dose of ¹³¹I caused by some form of cell damage from the diagnostic dosage of the radionuclide. Stunning could potentially reduce the therapeutic efficacy of ¹³¹I given to ablate a postthyroidectomy remnant. This study examines the outcomes of ablative ¹³¹I therapy after diagnostic studies with either ¹²³I or ¹³¹I to determine if the diagnostic dosages of these radionuclides used in our Thyroid Cancer Center reduce the efficacy of ¹³¹I given for remnant ablation. Methods: Fifty patients with nonmetastatic papillary or follicular carcinoma of the thyroid received total thyroidectomy; this was followed by thyroid hormone withdrawal to achieve a serum thyroid-stimulating hormone level in excess of 30 µIU/mL. They were divided prospectively into 2 groups. Group 1 had diagnostic imaging with 14.8 MBq of ¹²³I followed by thyroid remnant ablation with 3.7 GBq of ¹³¹I. Group 2 had empiric ablation with the same 3.7-GBq ¹³¹I dosage, but the preceding diagnostic scan was performed with 74 MBq of ¹³¹I. Comparisons of equivalence of the 2 population samples and of the postablation outcomes were evaluated by ² analysis. Successful ablation required a negative follow-up thyroid scan 6–8 mo after ablation and also an undetectable serum thyroglobulin level in the absence of antithyroglobulin antibodies. Results: There was no significant difference between the 2 groups demographically, in tumor burden or stage, or in the postthyroidectomy ablation rate (group 1, 81%; group 2, 74%; P > 0.05). Conclusion: If thyroid remnant stunning occurs due to 74 MBq ¹³¹I used as a diagnostic agent before ¹³¹I ablation, it has no significant clinical correlate, as it yields the same ablation rate as that which occurs after 14.8 MBq of ¹²³I used for imaging.

Key Words: thyroid carcinoma • ablation • stunning • ¹²³I-iodine • ¹³¹I-iodine

COPYRIGHT © 2007 by the Society of Nuclear Medicine, Inc.

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				N. A. Johnson and M. E. Tublin Postoperative Surveillance of Differentiated Thyroid Carcinoma: Rationale, Techniques, and Controversies Radiology, November 1, 2008; 249(2): 429 - 444. [Abstract] [Full Text] [PDF]

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				E. B. Silberstein Reply: Radioiodine Ablation Outcomes After Imaging with 123I or 131I: Is No News Good News? J. Nucl. Med., January 1, 2008; 49(1): 166 - 167. [Full Text] [PDF]