Impact of SPECT and integrated low-dose CT after radioiodine therapy on the management of patients with thyroid carcinoma

Juri Ruf, Lukas Lehmkuhl, Helga Bertram, Dirk Sandrock, Holger Amthauer, Beatrice Humplik, Dieter Ludwig Munz, Roland Felix
Nuclear Medicine Communications 2004, 25 (12): 1177-82

AIM: To determine the value of single photon emission computed tomography (SPECT) with integrated low-dose computed tomography (CT) for the interpretation of inconclusive foci in planar I whole-body scans after radioiodine therapy.

METHODS: Twenty-five patients with inconclusive findings in planar scanning after ablative radioiodine therapy (3.7 GBq I) due to differentiated thyroid cancer were included. SPECT/CT of the region in question was performed with the Millennium VG Hawkeye (GE Medical Systems). SPECT with and without CT fusion were evaluated by two blinded independent nuclear medicine physicians in a consensus reading (including visual plausibility control). Each focus was judged according to its topographical assignment and clinical interpretation. With regard to therapeutic relevance, this information was evaluated in a focus based and patient based analysis. All evaluations used a binary ranking system. Focus assignments were compared to clinical and imaging follow-up.

RESULTS: Forty-one lesions were observed in 25 patients. According to follow-up, 17/41 (41%) foci were caused by thyroid residue, 13/41 (32%) were caused by metastases, and 11/41 (27%) were not malignant. Of these foci, a SPECT/CT consensus reading assigned 39 (95%) correctly, as fused images of two foci did not pass the visual plausibility control (excluding one patient due to misregistration). For the remaining 39 foci, improved anatomical assignment by SPECT/CT was seen in 17/39 (44%) cases.

CONCLUSIONS: The changed interpretation of 15/39 (38%) foci would have been relevant for therapy in the focus based analysis. In the patient based analysis the information was still therapeutically relevant in 6/24 (25%) patients. Furthermore, plausibility control is also crucial in SPECT/CT image fusion in order to rule out artifacts.

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