Technetium-99m-pertechnetate whole-body SPET/CT scan in thyroidectomized differentiated thyroid cancer patients is a useful imaging modality in detecting remnant thyroid tissue, nodal and distant metastases before 131 I therapy. A study of 416 patients.

OBJECTIVE: In this study we aimed to evaluate the role of technetium-99m pertechnetate whole body scan (99m Tc 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 (131 I) therapy.

SUBJECTS AND METHODS: A retrospective analysis was performed in 416 pathologically confirmed DTC patients with total/near-total thyroidectomy. All patients had undergone 99m Tc WBS, followed by 131 I therapy and post therapy scans, under thyroid hormone withdrawal protocol. Eighteen patients had an additional 99m Tc SPET/CT of certain lesions. Foci of uptake on the 99m Tc WBS and when indicated additional foci on the SPET/CT scan were assessed and compared with findings from post-therapy 131 I scans study which served as gold standard.

RESULTS: The 99m Tc 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 99m Tc WBS to 99m Tc SPET/CT findings, 2/18 patients were confirmed as false-positive.

CONCLUSION: Our findings suggested that 99m Tc WBS is a useful imaging modality in detecting remnant thyroid tissue, nodal and distant metastases before 131 I therapy. The additional SPET/CT scan when needed in 18 cases supported the 99m Tc WBS diagnosis.