Material and Method: RxWBSs and SPECT/CT images of 93 consecutive patients were reviewed retrospectively by three experienced nuclear medicine physicians without knowledge of clinical data. RxWBSs were reviewed first followed by evaluation of RxWBS plus SPECT/CT imaging. Foci of increased radioiodine uptake were identified and localization was attempted. The findings obtained from RxWBS were compared with WBS plus SPECT/CT imaging to determine impact on lesion characterization, TNM staging, and management plan.

Results: Two hundred seventy seven lesions were identified by RxWBS alone. RxWBS plus SPECT/CT imaging detected eight additional pathologic lesions (4 in bones, two in neck, and one in lung and thyroid bed). RxWBS plus SPECT/CT studies reclassified 85 of 277 lesions (30.7%) detected by RxWBS. Most change occurred in neck region (57 lesions) followed by chest region (16 lesions). For impact on TNM staging, RxWBS plus SPECT/CT studies changed N stage of 21 patients (22.6%) and reclassified M stage of 10 patients (10.8%). These resulted in change of TNM stage group of 14 patients (15.1%) and changed management plan of 19 patients (20.4%).

Conclusion: The addition of SPECT/CT imaging to RxWBS in patients with differentiated thyroid cancer improved disease localization and lesion characterization leading to more accurate N and M staging, which was mainly downstaged. SPECT/CT also had impact on plan of management in about one fifth of the patients. However, caution should be taken when interpreting lesion in lower chest and upper abdomen because misregistration of SPECT and CT images.

Keywords: Radioiodine therapy, Single-photon emission computed tomography, SPECT/CT imaging, Radioiodine scan, Differentiated thyroid cancer