Aim: To determine the impact of SPECT/CT in lesion detection and its influence on TNM staging, when associated with whole-body radioiodine (WBI) scans in differentiated thyroid cancer (DTC) patients.
Material and Methods: Patients with pathologically proven DTC who underwent thyroidectomy with or without LN dissection and who have WBI imaging with SPECT/CT were enrolled in this study. Records were reviewed for patients' demographics, serum TSH, Tg and Tg antibodies levels, prior radioiodine ablation, histopathology and imaging results. After excluding physiological tracer distribution, radioiodine uptake was classified as positive, or equivocal in thyroid bed (TB), cervical lymph nodes (LN), or distant metastases (DM). SPECT/CT results were analyzed for added or excluded lesions and translated to changes in TNM staging.
Results: We included 48 patients (mean age; 46.9±18.7 years). In 20 patients, SPECT/CT was able to detect/confirm additional 45 lesions (4 TB, 22 LN, and 19 DM). SPECT/CT decreased number of equivocal results by 87% from 54 lesions to only 7 lesions, achieving definitive diagnosis in 41 patients (85.4%) compared to only 10 patients (20.8%) on planar images (p<0.0001). This was translated to TNM up-staging in 8 patients, and down-staging in 7 patients. Both Tg and age were positively correlated to number of SPECT/CT added lesions (0.601; p<0.0001 and 0.375; p=0.009 respectively). Cutoff values of Tg≥3.4 ng/ml and age>45 years were the best to predict additional lesions on SPECT/CT with sensitivity, specificity, and accuracy of 95, 75, & 87.5% and 80, 71.4, & 75% respectively (p<0.01 for both). No TNM up-staging was noted in patients with Tg<3.4 ng/ml.
Conclusion: SPECT/CT imaging was found to be superior to planar imaging in terms of detecting additional lesions, improving sensitivity and reducing number of equivocal lesions, improving specificity. SPECT/CT was able to significantly influence the TNM staging, with no up-staging noted in patients with Tg<3.4.