124I PET/CT in the pretherapeutic staging of differentiated thyroid carcinoma: comparison with posttherapy 131I SPECT/CT

Purpose

To compare pretherapy ¹²⁴I PET/CT and posttherapy ¹³¹I SPECT/CT in the identification of pathological lesions and the staging of patients with differentiated thyroid carcinoma.

Methods

¹²⁴I SPECT with low-dose CT in addition to a standard whole-body scan was performed 5 days following ¹³¹I therapy with the administration of 1,110–7,728 MBq. Pretherapy ¹²⁴I PET/CT was done 24 h and 96 h after oral ingestion of 20–28 MBq, including a noncontrast high-dose CT scan. Scans were evaluated by two independent experienced nuclear physicians. In addition to the total number of lesions found, patient-based analyses and lesion-based analyses were performed to ascertain the discrepancies between the findings of the two scanning techniques, as well as to evaluate the clinical impact of the findings.

Results

A group of 20 consecutive patients were analysed. In the lesion-based analysis, a total of 62 foci were found with all modalities together. Of these, ¹²⁴I PET/CT found 57 (92 %), ¹³¹I SPECT/CT 50 (81 %) and planar imaging 39 (63 %). In the patient-based analysis, in 50 % of patients complete concordance between the findings of ¹²⁴I PET and ¹³¹I SPECT was seen, in 5 % complete discordance and in the remaining 45 % partial discordance, i.e. a focus or some foci seen with both modalities but another or others seen more or less with one or other modality. In 5 of the 20 patients (25 %), tumour stage was changed according to the findings of one of the modalities. In 60 % of these patients this was only with the findings of ¹²⁴I PET/CT.

Conclusion

This study showed that ¹²⁴I PET/CT is preferred over ¹³¹I imaging for staging differentiated thyroid carcinoma.