The diagnostic value of 124I-PET in patients with differentiated thyroid cancer.

Background: The purpose of this prospective study was to evaluate the clinical diagnostic value of iodine-124 (124I)-positron emission tomography (PET) in patients with advanced differentiated thyroid carcinoma (DTC) and to compare the 124I-PET imaging results with the 131I whole-body scan (WBS).

Materials And Methods: Twenty patients with histologically proven advanced DTC (including T4, extra-nodal tumour growth, or distant metastases) underwent diagnostic 131I-WBS, 124I-PET scan, and post-treatment 131I-WBS 4 months after ablation. The findings on the 124I-PET were compared with the findings on the diagnostic and post-therapeutic 131I-WBS and were also correlated with radiologic and/or cytological investigations.

Results: 124 I-PET vs diagnostic 131 I-WBS. Eleven patients showed uptake on the 124I-PET. Only 3 of these 11 patients also showed uptake on the diagnostic 131I scan, but the uptake was more clearly visible and the abnormalities were more extensive on the 124I-PET. 124 I-PET vs post-treatment 131 I-WBS. Eleven patients showed uptake on the 124I-PET, which was also visible on the post-treatment scan in nine patients; in the other two patients, no uptake was observed on the post-treatment scan and no anatomical localisation could be confirmed. Two patients showed only uptake on the post-treatment scan without uptake on the 124I-PET: in one, the uptake was confirmed by MRI, and in the other, no anatomical localisation was found. In seven patients, no uptake was observed on both the scans.

Conclusion: 124I-PET proved to be a superior diagnostic tool as compared to low-dose diagnostic 131I scans and adequately predicted findings on subsequent high-dose post-treatment 131I scans.