Purpose: Hybrid imaging combining single photon emission computed tomography (SPECT) with (131)I and X-ray computed tomography (CT) performed at radioablation (RA) for thyroid carcinoma more accurately detects regional lymph node metastases (LNM) than does planar imaging. In this bicentric prospective study we used hybrid imaging in conjunction with histopathological examination to measure LNM frequency in a consecutive group of patients referred for RA due to stage T1 papillary thyroid carcinoma (PTC).
Methods: At the Departments of Nuclear Medicine of the Ludwig Maximilian University of Munich and the Friedrich Alexander University of Erlangen-Nuremberg SPECT/spiral CT is routinely performed in all PTC subjects at the time of RA. Screening of our SPECT/CT databases for PTC patients with T1 histology produced 98 patients from Munich and 53 patients from Erlangen, including 96 of 151 patients with microcarcinoma. In 69 patients of the entire group, cervical lymph node dissection had been performed, whereas nodal staging in the remaining 82 subjects was based on SPECT/CT.
Results: LNM incidence in the whole group was 26% [95% confidence interval (CI): 20-33%] versus 22% (95% CI: 15-31%) in the microcarcinoma subgroup. SPECT/CT was more accurate in 24.5% of our patients than planar imaging with regard to nodal staging.
Conclusion: LNM occurs in one quarter of all patients with T1 PTC, and also in the subset with microcarcinoma. Performing (131)I SPECT/CT, either with therapeutic or diagnostic radioactivities, directly after thyroidectomy should provide more accurate staging of T1 PTC, thus facilitating optimal therapeutic management.