Evaluation of Diagnostic Value of SPECT/CT Imaging in Post-radioiodine Therapy in Thyroid Cancer

This study aimed to investigate the value of single photon emission computed tomography/computed tomography (SPECT/CT) imaging in well-differentiated thyroid cancer (DTC) after radioiodine (I-131) ablation/therapy for clinical staging and risk stratification. It also aimed to determine whether SPECT/CT would change the management plan or predict the clinical outcomes of DTC patients.

A total of 78 DTC patients underwent first post radioiodine therapy "Whole body iodine-131 scintigraphy (WBS) along with SPECT/CT" at the Department of Radiology and Molecular imaging, Sultan Qaboos University Hospital, Muscat, Oman, between January 2014 and August 2017. Differences between WBS and SPECT/CT, change in clinical staging, risk stratification and management were recorded. The clinical outcome at 6-12 months was recorded. A generalised McNemar test was used to assess disagreement between WBS and SPECT/CT.

According to the American Thyroid Association (ATA) risk stratification, the sample showed low (35.8%), intermediate (53.8%) and high-risk groups (10.2%) on WBS, which changed to 44.8%, 38.4% and 16.6%, respectively, on SPECT/CT imaging. Overall change in risk stratification was noted in 16.7% and TNM stage in 11.5% of patients after SPECT/CT imaging. SPECT/CT changed the therapeutic plan and clinical outcome in 19.2% of patients.

SPECT/CT allows better detection and characterisation of metastatic lymph nodes and distant metastasis in DTC patients compared to WBS imaging alone. It alters TNM staging, ATA risk classification and management in a significant number of patients. It is recommended that SPECT/CT should be done routinely along with WBS in well-differentiated thyroid carcinoma.