Clinical applications of SPECT/CT after first I-131 ablation in patients with differentiated thyroid cancer

Summary Objective This study aimed to determine which thyroid cancer patients would benefit from SPECT/CT in addition to whole‐body planar scintigraphy (RxWBS) for the detection and characterization of I‐131 focal uptake after first ablation. Design and Patients Neck and thoracic SPECT/CT was performed in 187 patients with I‐131 focal uptake suggestive of remnant thyroid tissue (Rem group, n = 152) or presumed lymph node (LN) metastases (mLN group, n = 35) on RxWBS. Clinical and pathologic parameters were analysed and compared in patients with and without additional SPECT/CT findings. Results wIn the Rem group, SPECT/CT revealed additional occult findings on RxWBS in 13 patients (8·6%). The serum thyroglobulin levels at the time of ablation were significantly higher in patients with additional SPECT/CT findings than in patients without additional findings (4·3 ± 3·4 ng/ml vs 1·6 ± 2·7 ng/ml, P = 0·001). In the mLN group, SPECT/CT demonstrated only remnant thyroid tissues without evidence of lymph node metastasis in 14 (40·0%) patients, whereas in the remaining 21 (60·0%) patients, I‐131 uptake was confirmed in the corresponding neck and mediastinal lymph nodes on SPECT/CT. Conclusions Even in the Rem group, additional SPECT/CT could provide useful information for detecting hidden metastasis, especially in patients with high serum thyroglobulin levels. SPECT/CT should be recommended for patients with focal uptake lymph node metastasis on RxWBS.