Comparison of F-18-FDG, I-131-Na, and Tl-201 in diagnosis of recurrent or metastatic thyroid carcinoma

There are several reports about the usefulness of F-18-FDG PET in thyroid c ancer. However, few studies have compared FDG PET with I-131 and Tl-201 sci ntigraphy. The aim of this study was to evaluate the clinical significance of whole-body FDG PET in differentiated thyroid cancer and to compare the r esults with those obtained from I-131 and Tl-201 scintigraphy. Methods: Who le-body FDG PET was performed on 32 patients (10 men, 22 women; age range, 30-77 y; mean age, 54 y) with differentiated thyroid cancer (5 cases of fol licular cancer and 27 of papillary cancer) after total thyroidectomy. An ov erall clinical evaluation was performed, including cytology, thyroglobulin level, sonography, MRI, and CT, to allow a comparison with functional imagi ng results for each patient. Metastatic regions were divided into five area s: neck, lung, mediastinum, bone, and other. Multiple lesions in one area w ere defined as one lesion. The tumor-to-background ratio (TBR) was measured for the lesions that were positive for both Tl-201 uptake and FDG PET upta ke. Results: The number of lesions totaled 47, Forty-one (87%) were detecte d by all scintigraphic methods. FDG uptake was concordant with I-131 uptake in only 18 lesions (38%). FDG uptake was concordant with Tl-201 uptake in 44 lesions (94%), Only one lesion was negative for FDG uptake and positive for Tl-201 uptake, and two lesions were positive for FDG uptake and negativ e for Tl-201 uptake. A significant correlation was seen between the TBR of Tl-201 and that of FDG (r = 0.69; P < 0.05). Conclusion: These data indicat e that for detecting metastatic lesions, FDG PET and I-131 scintigraphy may provide complementary information, whereas FDG PET may provide results sim ilar to those of Tl-201 scintigraphy. Thus, the combination of I-131 scinti graphy and FDG PET (or Tl-201 scintigraphy) is the method of choice for det ecting metastatic thyroid cancer after total thyroidectomy.