Objective: In this study we aimed to evaluate the role of technetium-99m pertechnetate whole body scan (99mTc WBS) with single photon emission tomography/computed tomography (SPET/CT) in detecting remnant thyroid tissue, nodal and distant metastases, in differentiated thyroid cancer (DTC) patients before radioiodine (131I) therapy.
Subjects and methods: A retrospective analysis was performed in 416 pathologically confirmed DTC patients with total/near-total thyroidectomy. All patients had undergone 99mTc WBS, followed by 131I therapy and post therapy scans, under thyroid hormone withdrawal protocol. Eighteen patients had an additional 99mTc SPET/CT of certain lesions. Foci of uptake on the 99mTc WBS and when indicated additional foci on the SPET/CT scan were assessed and compared with findings from post-therapy 131I scans study which served as gold standard.
Results: The 99mTc WBS showed a sensitivity and positive predictive value of 79% and 100%, respectively, for remnant thyroid tissue detection, while 60% and 98%, respectively for metastatic lymph nodes evaluation. High specificity (99%) and negative predictive value (93%) but low sensitivity (37%) was found in detecting distant metastases. By adding 99mTc WBS to 99mTc SPET/CT findings, 2/18 patients were confirmed as false-positive.
Conclusion: Our findings suggested that 99mTc WBS is a useful imaging modality in detecting remnant thyroid tissue, nodal and distant metastases before 131I therapy. The additional SPET/CT scan when needed in 18 cases supported the 99mTc WBS diagnosis.