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

Background The purpose of this prospective study was to evaluate the clinical diagnostic value of iodine- 124 ( I-124)positron emission tomography ( PET) in patients with advanced differentiated thyroid carcinoma ( DTC) and to compare the I-124- PET imaging results with the I-131 wholebody scan ( WBS).Materials and methods Twenty patients with histologically proven advanced DTC ( including T4, extra- nodal tumour growth, or distant metastases) underwent diagnostic (IWBS)-I-131, I-124- PET scan, and post-treatment I-131- WBS 4 months after ablation. The findings on the I-124- PET were compared with the findings on the diagnostic and post-therapeutic I-131- WBS and were also correlated with radiologic and/ or cytological investigations.Results I-124- PET vs diagnostic I-131- WBS. Eleven patients showed uptake on the I-124- PET. Only 3 of these 11 patients also showed uptake on the diagnostic I-131 scan, but the uptake was more clearly visible and the abnormalities were more extensive on the I-124- PET. I-124- PET vs post-treatment I-131- WBS. Eleven patients showed uptake on the I-124- 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 I-124- 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 I-124- PET proved to be a superior diagnostic tool as compared to low-dose diagnostic I-131 scans and adequately predicted findings on subsequent high-dose post-treatment I-131 scans.