Lisanne de Koster

348 chapter 5 Visual [18F]FDG-PET/CT assessment Thirty-one of 33 (94%) malignant/borderline nodules and 53 of 90 (59%) benign nodules were visually [18F]FDG-positive. The median SUV max was 7.1 g/mL (IQR, 3.9-13.9) in [ 18F]FDG-positive and 2.3 g/mL (IQR, 1.9-2.8) in [18F]FDG-negative nodules. Two low-risk malignancies (one pT1bN0 and one pT2N0) were [18F]FDG-negative (false-negative). The diagnostic accuracy of visual [18F]FDG-PET/CT assessment in the current study was similar to the original trial (n=132) (Table 2) [501]. All but one of 29 Hürthle cell nodules were visually [18F]FDG-positive, resulting in a 3.4% benign call rate (Table 2). Quantitative [18F]FDG-PET/CT assessment In all 123 nodules, the median SUVmax, SUVpeak, SUVmax-ratio and SUVpeak-ratio were significantly higher in malignant/borderline nodules than in benign nodules (p<0.001) (Table 3). ROC curve analysis showed similar AUCs for all SUV-metrices (Figure 3). A 97.0% sensitivity was reached at SUVmax, SUVpeak, SUVmaxratio and SUVpeak-ratio cut-offs of 2.1 g/mL, 1.6 g/mL, 1.2, and 0.9, respectively (Table 2). At these cutoffs, the benign call rate varied between 8.9% for the SUVpeak and 28.5% for the SUVmax-ratio. Missed malignant/borderline tumours varied across the SUV-metrices and included the two visually falsenegative nodules and a 20 mm NIFTP with a SUVmax of 2.1 g/mL and SUVpeak of 1.6 g/mL. In the 94 non-Hürthle cell nodules, a sensitivity of 95.8% was established at the same cut-offs, with the benign call rate ranging from 10.6% to 35.1% (Table 2). Similar cut-offs for all SUV metrices and similar benign call rates were found in AUS/FLUS as compared to FN/SFN nodules (Tables 2 and 3, figure 3). In the 29 Hürthle cell nodules, no significant differences in SUV-metrices were found between malignant/borderline and benign nodules (Table 3). The AUCs ranged from 0.533 for the SUVmax to 0.700 for the SUVpeak-ratio (Figure 3). Yet, at SUV cut-offs of 5.2 g/mL, 4.7 g/mL, 3.4, and 2.8, sensitivity was 100% with benign call rates ranging from 17.2% for the SUVmax to 24.1% for the SUVpeak and SUVpeak-ratio (Table 2). Subgroup analysis of the visually [18F]FDG-positive non-Hürthle cell nodules showed similar SUV values in malignant/borderline and benign nodules. Threshold analysis in this subgroup showed that a ≥95% sensitivity was only achieved at minimal benign call rates (Table 3 and 6). Radiomic analysis The 84 (68%) patients with visually [18F]FDG-positive nodules were included in the radiomic analysis, including 56 (67%) non-Hürthle and 28 (33%) Hürthle cell nodules (Figure 1). Dimensionality reduction of the radiomic feature set retained six factors in every training set (68 patients in training sets). The mean AUC of the PET model was 0.445 in the test set (Figure 4, Table 6). The retained factors

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