Delayed acquisition 18F-FDG PET-CT assessment in differentiating brain metastasis recurrence and radiation-induced necrosis

Objective. - To assess the contribution of delayed F-18-FDG positron emission tomography computed tomography (PET/CT) for to the differential diagnosis between brain metastasis relapse and radiation-induced necrosis (RIN). Patients and methods. - Thirty-nine patients treated with radiotherapy for cerebral metastases and under suspicion of tumor recurrence underwent a dual phase F-18-FDG PET/CT. Images were reviewed randomly, retrospectively, with morphological MRI co-registration. An increased uptake of F-18-FDG was visually sought for 30 min and 4 hours after the F-18-PDG injection. The SUVmax, measured within the assessed lesion and within a contralateral control area, allowed for a lesional uptake semi-quantification, at early time (nSUVp) and delayed time (nSUVt), with a normalized retention index (nIR). Outcome was clinical and morphological MRI follow-up data, MR spectroscopy and histology. The sensitivity and specificity were computed relatively to a composite endpoint including histological, clinical, SRM and MRI follow-up data. Results. - Forty-nine lesions were analyzed. Nine lesions were investigated with histology, all concluding to malignancy. Seven were positive at early time and all nine of them were positive at delayed time. Delayed F-18-FDG PET/CT lead to 11 more lesion diagnoses than the early acquisition on its own, which represents an increase in sensitivity from 57% to 93%, without specificity loss (93%). Finally, the nSUVp, nSUVt and nIR were significantly higher in the tumor recurrence group than in the RIN group. Conclusions. - The delayed acquisition is a simple technique, drastically increasing the sensitivity of F-18-FDG PET/CT for detecting tumor relapse, without specificity loss. (C) 2016 Elsevier Masson SAS. All rights reserved.