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

Abstract

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.

Fig. 1

The diagram showed a schematic course of the investigations performed 4 months after ablation

Fig. 2

This patient (no. 1) showed a clearly visible lesion in the cervical vertebrae on the ¹²⁴I-PET (a, arrow), comparable with the lesion visible on the post-treatment ¹³¹I-WBS (c, arrow). This lesion was vaguely visible on the diagnostic ¹³¹I-WBS (b, arrow). Physiologic uptake in the esophagus, gastrointestinal tract and bladder is observed on the ¹²⁴I-PET

Fig. 3

This patient (no. 6) showed a clearly visible lesion in the left lower neck region or on the ¹²⁴I-PET (a, arrow), comparable with the lesion visible on the post-treatment ¹³¹I-WBS (c, arrow). No uptake was observed on the diagnostic ¹³¹I-WBS (b)

Fig. 4

Clearly, uptake in the right costae (arrow) and left hip is seen on the FDG-PET (c) in patient no. 11, whereas the post-treatment ¹³¹I-WBS (a) was negative. The ¹²⁴I-PET (b) showed only uptake around the femur prosthesis on the right side, which is also observed on the FDG-PET, which could be explained by reactive tissue on the MRI. The complementary uptake of radioiodine and FDG is also known as the flip-flop phenomenon, which was first described by Joensuu and Ahonen [27]