131I-SPECT/CT in neck lymph node metastasis detection in patients with differentiated thyroid carcinomas (DTC) in long-term follow-up

PO085
131I-SPECT/CT in neck lymph node metastasis
detection in patients with differentiated thyroid
carcinomas (DTC) in long-term follow-up
A. Marongiu1, S. Nuvoli2, I. Gelo2, L. Mele2, B. Piras2, M.L. Stazza2,
S. Galassi2, G. Madeddu2, A. Spanu2
1Unit of Nuclear Medicine, Department of Clinical, Surgical and
Experimental Sciences, University of Sassari, Sassari, Italy. 2Unit of
Nuclear Medicine, Department of Clinical, Surgical and Experimental
Sciences, University of Sassari, Sassari, Italy
Background-aim: The prognostic importance of regional lymph
node metastases in DTC is controversial even if it is generally
accepted that their presence, especially if in bilateral regions, correlates
with tumor recurrences and with adverse prognosis, in particular
in older age group. Thus, their identification is mandatory to achieve
early the most appropriate treatment. We further investigated the
usefulness of 131I-SPECT/CT with diagnostic dose in neck lymph
node metastasis detection in DTC patients in long term follow-up.
Methods: We retrospectively evaluated 215 consecutive DTC
patients already submitted to total thyroidectomy and radioiodine
therapy, all of them with ascertained radioiodine avid foci in the neck
at 131I-SPECT/CT during long-term follow-up; at surgery, 62
patients were classified at high risk (H), 61 at low risk (L), 92 at very
low risk. All patients underwent 131I-whole body scanner (WBS)
followed by SPECT/CT 48 h after an orally radioiodine administered
dose of 185 MBq, using a hybrid variable dual head gamma camera,
including a low dose-x-ray, and equipped with high energy, parallel
hole collimators.
Results: SPECT/CT detected 456 iodine avid foci in the neck in the
215 patients, while WBS evidenced 323 foci in 161/215, patients all
also identified by SPECT/CT.WBS classified as residues 262/323 foci
and as unclear 61 foci. SPECT/CT confirmed 253/262 foci as residues
but correctly characterized the remaining 9 cases as 8 neck lymph
node metastases and 1 physiologic structure. Moreover, SPECT/CT
appropriately characterized the 61 foci unclear at WBS as 18 lymph
node metastases, 24 residues and 19 iodine avid physiologic structures.
In 73 patients, SPECT/CT also detected 133 occult foci at
WBS, among whom 54 cases with foci completely occult at WBS,
characterizing these as 59 residues and 74 lymph node metastases.
Globally, SPECT/CT identified 100 metastatic foci as neck lymph
node metastases in 54 patients (23 H, 11L, 20VL), while WBS evidenced
26 (p\0.0001) in 22 cases, in part wrongly classified as
residues and in part as unclear foci. Twelve VL patients, seven of
whom with lymph nodes near submandibular glands, had thyroglobulin
undetectable or\2.5 ng/ml and were T1aN0M0. Globally,
SPECT/CT obtained an incremental value than WBS in 43.2% of
cases, a more correct patient classification changing therapeutic
approach in 27.4% of cases and contributed to avoid unnecessary therapies in presence of single foci of physiologic uptakes not classified
by WBS in 7% of cases.
Conclusions: 131I-SPECT/CT proved a reliable tool in detecting and
characterizing neck lymph node metastases in DTC patients in long term
follow-up improving WBS performance, including the interpretation
of unclear foci, and reducing the false positive results. The
role of SPECT/CT appears particularly significant in patients with
WBS inconclusive, VL, T1aN0MO and with undetectable or very low
thyroglobulin levels.