Incremental value of 131 I SPECT-CT versus planar whole body imaging in patients with differentiated thyroid carcinoma

Objectives: To evaluate the incremental diagnostic value of iodine-131 single-photon emission computed tomography/computed tomography ( 131 I SPECT-CT) compared to planar scintigraphy in patients with differentiated thyroid carcinoma (DTC). Materials and Methods: The study group consisted of 117 patients (Age group = 7-81 yrs; 70 females, 47 males) with DTC; post total thyroidectomy. A diagnostic dose of 111 Mbq (3 mCi) 131 I was administered and planar scan obtained after 48 hrs. Foci of uptake in planar scan were classified as thyroid remnants, lymph nodes, lung metastases, skeletal metastases, distant metastases or of indeterminate etiology. Single-photon emission computed tomography/computed tomography (SPECT-CT) of these areas was then acquired on a dual head gamma camera and reclassification was done. Results: Planar scans depicted 218 foci of 131 I activity classified as 194 neck foci and 24 distant foci. Incremental value of SPECT/CT compared with planar imaging was found for 72 of 194 neck lesions (37.1%) and 24 of 24 distant foci (100%) for a total of 95 of 218 iodine avid foci (44%). SPECT/CT findings led to down staging of 44 of the 72 foci from equivocal or lymph nodes to thyroid remnant and upstaging of 18 of the 72 foci from equivocal or thyroid remnant to lymph node involvement. An additional 8 of the 72 foci were reclassified as physiologic dental or salivary gland activity. The remaining 2 of the 72 foci was found out to be contamination on patient's skin. Conclusion: 131 I SPECT-CT provides increased diagnostic information compared with planar imaging alone, which may alter the patient management.