Can calcification predict 131I accumulation on metastatic lymph nodes in papillary thyroid carcinoma patients receiving 131I therapy? Comparison of CT, 131I WBS and 18F-FDG PET/CT

The aim of this study was to clarify the predictive significance of nodal calcification in terms of the therapeutic option of I-131 therapy in papillary thyroid carcinoma (PTC) patients. We reviewed 19 computed tomography (CT) examinations of PTC patients on receiving I-131 therapy for the presence of nodal calcification, and compared the I-131 whole-body scintigraphy and F-18-2-fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET)/CT findings. The metastatic lymph nodes (mLNs) were divided into three groups: A, those with calcification; B, those without calcification but belonging to patients who had calcified mLNs; C, those without calcification and belonging to patients who had no calcified mLNs. The incidences of I-131 accumulation and maximum standardised uptake values (SUV max) in the three groups were compared. A total of 70 mLNs were evaluated. Twelve mLNs belonged to group A, 13 to group B and 45 to group C. The incidences of I-131 accumulation were significantly higher in groups A (100%) and B (100%) than in group C (11.1%) (p < 0.0001 for both). The SUVmax was significantly lower in groups A (4.1 +/- 1.9) and B (3.9 +/- 1.4) than in group C (7.1 +/- 4.4) (p = 0.01, p = 0.002, respectively). Our results indicated that calcification in mLNs related to the ability of I-131 accumulation and less dedifferentiation.