Impact of SPECT and integrated low-dose CT after radioiodine therapy on the management of patients with thyroid carcinoma.
OBJECTIVE
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.
Ruf
Juri
J
Klinik für Strahlenheilkunde bKlinik für Nuklearmedizin, Charité-Universitätsmedizin Berlin, Germany. juri.ruf@charite.de
Lehmkuhl
Lukas
L
Bertram
Helga
H
Sandrock
Dirk
D
Amthauer
Holger
H
Humplik
Beatrice
B
Ludwig Munz
Dieter
D
Felix
Roland
R
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D009362:Neoplasm Metastasis; D019275:Radiopharmaceuticals / Q000627:therapeutic use*; D013964:Thyroid Neoplasms / Q000175:diagnosis* / Q000532:radiotherapy*; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals