Clinical Utility of F-18-FDG PET/CT Concurrent with I-131 Therapy in Intermediate-to-High-Risk Patients with Differentiated Thyroid Cancer: Dual-Center Experience with 286 Patients

Abstract

Patients with differentiated thyroid carcinoma (DTC) are treated with I-131 therapy after total thyroidectomy or surgical resection of recurrent tumor. However, some recurrent DTC lesions are not iodine-avid, which affects further treatment planning. The aim of this study was to evaluate the clinical benefit of F-18-FDG PET/CT performed concurrently with I-131 therapy in DTC patients with intermediate to high risk. Methods: We retrospectively enrolled 286 DTC patients at 2 Korean medical centers who comprised 2 different patient groups: 28 patients who underwent adjuvant I-131 treatment after curative surgical resection of recurrent tumor and 258 patients with intermediate to high risk who underwent I-131 ablation after total thyroidectomy. I-131 therapy and F-18-FDG PET/CT scanning were performed on the same day. Administration of L-thyroxine was withheld from all enrollees for 4 wk before I-131 treatment. Results: In 39 patients (14%), F-18-FDG PET/CT detected additional recurrent or metastatic lesions that were not detected on the posttherapy I-131 scan, and the treatment plan was changed for 30 patients (10%) based on such findings. Among the 28 patients receiving I-131 treatment after resection of recurrent tumor, PET/CT detected additional lesions in 46%, and treatment was changed in 43%. Assessing a subgroup of stage T3-T4N1 patients with tumor size > 2.0 cm, among 258 patients undergoing I-131 ablation after total thyroidectomy, we found that 25% had additional positive PET/CT results, and treatment changed for 17%. In contrast, 8% of stage T3-T4N1 patients with tumor size <= 2.0 cm, 6% of stage T1-T2N1 patients, and 3% of stage T3-T4N0 patients had additional positive PET/CT findings. Conclusion: F-18-FDG PET/CT performed concurrently with I-131 therapy detected additional lesions in 14% of DTC patients and was particularly helpful for detecting additional lesions in patients undergoing I-131 therapy after resection of recurrent tumor or in stage T3-T4N1 patients with tumor size > 2.0 cm.