FOLLOW-UP OF DIFFERENTIATED THYROID-CANCER - WHAT IS THE VALUE OF FDGAND SESTAMIBI IN THE DIAGNOSTIC ALGORITHM

Aim: FDG-PET and MIBI-scintigraphy with SPECT were compared to [I-131] -whole-body scintigraphy (WBS) and morphologic imaging in the follow-u p of differentiated thyroid cancer. Their influence on therapy-plannin g was analysed. Methods: In 50 consecutive patients (papillary/ follic ular/variants of a follicular carcinoma: 33/13/4: primary status: pT1/ 2/3/4: 3/16/9/22) FDG-PET of neck/chest and MIBI-whole-body scan inclu ding SPECT were performed during hypothyreosis and before WBS. Morphol ogic imaging was done by MRI in all and by CT of the lung without cont rast media in 21 patients. Results: The complete extent of metastases was detected by FDG-PET in 11 and by MIBI-scintigraphy also in 11 of 2 2 patients with evidence of disease, The combined evaluation of WBS an d FDG-PET as well as of WBS and MIBI-scintigraphy held true in 18 of 2 2 patients. Limiting FDG-PET or MIBI-scintigraphy to patients with ele vated thyroglobulin (Tg)-levels and negative WBS only, would not, ther efore. alter the sensitivity oi this algorithm. The diagnostic benefit of FDG-PET and MIBI-scintigraphy was confined to lymph node metastase s. The 1 cm limit for lymph node size in morphologically based imaging did not apply to FDG-PET and MIBI-scintigraphy. None of the 6 patient s with small (<1 cm) pulmonary metastases showed either FDG- or MIBI-u ptake, but could be diagnosed by spiral-CT. Conclusion: WBS cannot be replaced by FDG-PET or MIBI-scintigraphy; neither of the latter was be tter than the other. Rising Tg-levels, negative WBS and the exclusion of pulmonary metastases by spiral-CT define the constellation in which FDG-PET and MIBI-scintigraphy can provide data of therapeutic relevan ce.