Various studies have compared the detection of functioning residual thyroid tissue after thyroidectomy using radioiodine whole-body (WB) imaging following preparation of patients with injections of recombinant human thyroid-stimulating hormone (rhTSH) and thyroid hormone withdrawal (THW). However, metastases may have radiopharmacokinetics different from normal thyroid tissue. The objective of this study was to evaluate these 2 methods of patient preparation for the detection of metastases from differentiated thyroid cancer (DTC) using (131)I WB imaging and (124)I PET.
Methods: A prospective study approved by the institutional review board was conducted at Washington Hospital Center from 2006 to 2010 recruiting patients who had DTC, were suspected of having metastasis from DTC (e.g., elevated thyroglobulin level without thyroglobulin antibodies, positive results on recent fine-needle aspiration, suspected enlarging mass, and abnormal findings suggesting metastasis on a diagnostic study) and were referred for (131)I WB dosimetry. All patients subsequently underwent both (131)I WB imaging and (124)I PET performed using the same preparation. All foci of uptake identified on these scans were categorized in a masked manner by consensus of 2 physicians in the following manner: 1, definite physiologic uptake or artifact; 2, most likely physiologic uptake or artifact; 3, indeterminate; 4, most likely locoregional metastases in the neck bed; 5, most likely distant metastases; or 6, definite distant metastases. Foci categorized as 4, 5, and 6 were considered positive for functioning metastases.
Results: Of 40 patients evaluated, 24 patients were prepared with rhTSH and 16 with THW. No statistical difference was noted between the 2 groups for any of the parameters evaluated, including serum thyroglobulin. The percentages of patients with positive foci detected on the rhTSH (131)I and THW (131)I WB scans were 4% (1/24) and 63% (10/16), respectively (P < 0.02). The number of foci detected on the rhTSH (131)I and THW (131)I WB scans were 2 and 58, respectively (P < 0.05). When (124)I PET was used for imaging, the percentages of patients with foci detected on the rhTSH and THW scans were 29% (7/24) and 63% (10/16), respectively (P < 0.03). The number of foci detected on the rhTSH and THW scans were 17 and 117, respectively (P < 0.03).
Conclusion: Significantly more foci of metastases of DTC may be identified in patients prepared with THW than in patients prepared with rhTSH.