Incremental diagnostic value of SPECT/CT with 131I scintigraphy after radioiodine therapy in patients with well-differentiated thyroid carcinoma.

PURPOSE To retrospectively determine the incremental diagnostic value of adding single photon emission computed tomography/computed tomography (SPECT/CT) to whole-body scintigraphy with iodine 131 ((131)I) compared with scintigraphy alone after radioiodine therapy in patients with well-differentiated thyroid carcinoma. MATERIALS AND METHODS This retrospective study was institutional review board approved; written informed consent was waived. The study included 147 patients (94 female, 53 male patients; mean age, 51 years) with well-differentiated thyroid carcinoma treated with radioiodine therapy between October 2009 and August 2010. Whole-body scintigraphy and SPECT/CT were performed on the same day in all patients receiving radioiodine therapy. Each radioactive focus at whole-body scintigraphy was classified as positive or equivocal with respect to thyroid bed, lymph node, and distant metastasis uptake. Differences between whole-body scintigraphy and SPECT/CT findings were assessed with the generalized McNemar test. RESULTS At SPECT/CT, origin was clearly determined of all five "hot spots" in the thyroid bed (remnant thyroid tissue or metastatic lymph node) that were judged as equivocal at whole-body scintigraphy. Interpretation of 24 (22.2%) of 108 radioactive foci for lymph node metastases was changed with SPECT/CT (P < .0001). One of 85 foci that were thought to be positive findings at whole-body scintigraphy turned out to be a negative finding (false-positive finding), and 13 and seven of 20 equivocal foci at whole-body scintigraphy were positive and negative findings, respectively, after adding SPECT/CT findings. Three false-negative findings at whole-body scintigraphy were corrected with SPECT/CT. For the detection of distant metastasis, the interpretations of 21 (40%) of 52 foci were corrected with SPECT/CT (P < .0001). One of 32 foci thought to be a positive finding at whole-body scintigraphy was a negative finding, and 11 and nine of 20 equivocal foci at whole-body scintigraphy were positive and negative findings, respectively, after SPECT/CT. At a patient-based analysis, SPECT/CT findings helped change the clinical staging in nine (6.1%) of 147 patients and therapeutic planning in three (2.0%) of 147 patients. CONCLUSION SPECT/CT improved detection and localization of (131)I accumulation in lymph node metastases and distant metastases, compared with whole-body scintigraphy.