Differentiated thyroid carcinoma (DTC) patients typically undergo thyroidectomy followed by therapeutic I-131 as the normal course of treatment, but not all DTC lesions respond to therapy. FDG PET/CT detected additional tumors in up to 46 percent of certain patients when performed concurrently with I-131 therapy. The method could help improve risk stratification for these patients by catching outlier lesions, according to a study published June 24 in the Journal of Nuclear Medicine.

Jeong Won Lee, MD, PhD, from the department of nuclear medicine at Yonsei University College of Medicine in Seoul, and colleagues conducted a retrospective study of 286 DTC patients at two medical centers to evaluate F-18 FDG PET/CT as a complement to I-131 therapy for patients with intermediate to high risk or remaining or recurrent disease.

“F-18 FDG PET/CT is useful for the detection of recurrent DTC lesions, especially in patients with iodine-negative tumors and elevated serum thyroglobulin levels,” wrote Lee et al. “Furthermore, recent studies showed that F-18 FDG PET can detect DTC lesions more accurately under thyroid-stimulating hormone (TSH) stimulation than under TSH suppression. Because I-131 treatment is performed in the context of an elevated serum TSH level, concurrent F-18 FDG PET with I-131 treatment could be beneficial for detecting recurrent DTC lesions, especially iodine-negative lesions, and for planning further treatment.”

The study was comprised of two separate patient groups. One included 28 patients who were administered adjuvant I-131 treatment following curative surgical resection of recurrent DTC tumor and another included 258 patients who underwent total thyroidectomy followed by I-131 ablation.

Both I-131 therapy and F-18 FDG PET/CT imaging were completed on the same day. Results showed 14 percent, or 39 patients had additional recurrent or metastatic lesions when imaged with FDG PET/CT that were not indicated as a result of post-therapy I-131 imaging. Patient management and treatment planning were altered for 10 percent of patients. PET/CT detected additional lesions in 46 percent of the 28 patients receiving I-131 treatment after resection of recurrent cancer. This led to additional treatment planning in 43 percent of these cases.