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Background: FDG-PET/CT has a high negative predictive value to detect residual nodal disease in patients with locally advanced squamous cell head and neck cancer after completing concurrent chemoradiotherapy (CCRT). However, the positive predictive value remains suboptimal due to inflammation after radiotherapy, generating unnecessary further investigations and possibly even surgery. We report the results of a preplanned secondary end point of the ECLYPS study regarding the potential advantages of dual time point FDG-PET/CT imaging (DTPI) in this setting. Standardized dedicated head and neck FDG-PET/CT images were obtained 12 weeks after CCRT at 60 and 120 min after tracer administration. We performed a semiquantitative assessment of lymph nodes, and the retention index (RI) was explored to optimize diagnostic performance. The reference standard was histology, negative FDG-PET/CT at 1 year, or > 2 years of clinical follow-up. The time-dependent area under the receiver operator characteristics (AUROC) curves was calculated., Results: In total, 102 subjects were eligible for analysis. SUV values increased in malignant nodes (median SUV 1  = 2.6 vs. SUV 2  = 2.7; P = 0.04) but not in benign nodes (median SUV 1  = 1.8 vs. SUV 2  = 1.7; P = 0.28). In benign nodes, RI was negative although highly variable (median RI = - 2.6; IQR 21.2), while in malignant nodes RI was positive (median RI = 12.3; IQR 37.2) and significantly higher (P = 0.018) compared to benign nodes. A combined threshold (SUV 1  ≥ 2.2 + RI ≥ 3%) significantly reduced the amount of false-positive cases by 53% (P = 0.02) resulting in an increased specificity (90.8% vs. 80.5%) and PPV (52.9% vs. 37.0%), while sensitivity (60.0% vs. 66.7%) and NPV remained comparably high (92.9% vs. 93.3%). However, AUROC, as overall measure of benefit in diagnostic accuracy, did not significantly improve (P = 0.62). In HPV-related disease (n = 32), there was no significant difference between SUV 1 , SUV 2 , and RI in malignant and benign nodes, yet this subgroup was small., Conclusions: DTPI did not improve the overall diagnostic accuracy of FDG-PET/CT to detect residual disease 12 weeks after chemoradiation. Due to differences in tracer kinetics between malignant and benign nodes, DTPI improved the specificity, but at the expense of a loss in sensitivity, albeit minimal. Since false negatives at the 12 weeks PET/CT are mainly due to minimal residual disease, DTPI is not able to significantly improve sensitivity, but repeat scanning at a later time (e.g. after 12 months) could possibly solve this problem. Further study is required in HPV-associated disease., (© 2022. The Author(s).)

Amyloid deposition can lead to Alzheimer disease and cerebral amyloid angiopathy. Rarely, it presents as a solitary focal deposition, primary cerebral amyloidoma, which can be misinterpreted as a neoplasm because of the "tumor-like" appearances. We present the case of a 54-year-old woman where MRI revealed a T2-hyperintense mass periventricular in the white matter with moderate contrast enhancement. Pathological investigation revealed AL (lambda) amyloidoma. F-florbetapir PET/CT was used to support the diagnosis and in follow-up. This case highlights that F-florbetapir PET/CT might play a role in the diagnostic workup of patients suggestive of cerebral amyloidoma, especially in cases where biopsy is not feasible.