Role of 18F-FDG PET/CT Concurrent with First 131I Therapy in High-Risk Differentiated Thyroid Cancer Patients: Preliminary Results.

  • BACKGROUND: ATA Guidelines for adult patients with differentiated thyroid cancer1 (DTC) defined 4 categories to classify radioiodine-refractory patients. 2 out of 4 categories are: presence of metastatic tissue which does not concentrate RAI at the first therapeutic whole-body scan (TxWBS); uptake of radioiodine in some lesions but not in others. Aim of the present study was to evaluate the performance 18F-FDG PET/CT concurrent with first radioiodine therapy (RAI) in high risk differentiated thyroid cancer (DTC) patients to predict radioiodine-refractory DTC distant metastases.

    METHODS: We prospectively selected patients classified as high risk by ATA 2015 Risk Stratification System1, submitted to total thyroidectomy and first RAI treatment. 13 patients, off L-T4, were submitted to PET/CT 3 months after surgery and within 1 week from RAI. The analysis of PET/CT and TxWBS images was performed only on distant metastases. Semi-quantitative analysis [standard uptake value (SUV), qPET, metabolic tumor volume (MTV) and total lesion glycolysis (TLG)] was performed on PET/CT target lesions (hottest lesion for each organ). ROC curve analysis was used to identify a potential cut-off for semi-quantitative parameters to predict radioiodine uptake.

    RESULTS: To semi-quantitative PET/CT analysis, target lesions with no radioiodine uptake, showed a value of SUVmax and qPET greater than 11.35 (AUC=0.9, p<0.001) and 4.56 (AUC=0.9, p<0.001) respectively. MTV and TLG thresholds were not able to predict which lesions had no RAI uptake.

    CONCLUSIONS: This preliminary work showed that PET/CT, performed concurrently with the first RAI in high-risk DTC patients, could be a promising method to early individuate RAI-refractory DTC patients.


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