Recurrent Glioblastoma Versus Late Posttreatment Changes: Diagnostic Accuracy Of O-(2-[F-18]Fluoroethyl)-L-Tyrosine Positron Emission Tomography (F-18-Fet Pet)

Background. Diagnostic accuracy in previous studies of O-(2-[F-18]-fluoroethyl)-L-tyrosine (F-18-FET) PET in patients with suspected recurrent glioma may be influenced by prolonged dynamic PET acquisitions, heterogeneous populations, different non-standard-of-care therapies, and PET scans performed at different time points post radiotherapy. We investigated the diagnostic accuracy of a 20-minute F-18-FET PET scan in MRI-suspected recurrent glioblastoma 6 months after standard radiotherapy and its ability to prognosticate overall survival (OS).Methods. In total, 146 glioblastoma patients with 168 F-18-FET PET scans were reviewed retrospectively. Patients with MRI responses to bevacizumab or undergoing re-irradiation or immunotherapy after F-18-FET PET were excluded. Maximum and mean tumor-to-background ratios (TBRmax, TBRmean) and biological tumor volume (BTV) were recorded and verified by histopathology or clinical/radiological follow-up. Thresholds of F-18-FET parameters were determined by receiver operating characteristic (ROC) analysis. Prognostic factors were investigated in Cox proportional hazards models.Results. Surgery was performed after 104 F-18-FET PET scans, while clinical/radiological surveillance was used following 64, identifying 152 glioblastoma recurrences and 16 posttreatment changes. ROC analysis yielded thresholds of 2.0 for TBRmax, 1.8 for TBRmean, and 0.55 cm(3) for BTV in differentiating recurrent glioblastoma from posttreatment changes with the best performance of TBRmax (sensitivity 99%, specificity 94%; P < 0.0001) followed by BTV (sensitivity 98%, specificity 94%; P < 0.0001). Using these thresholds, 166 F-18-FET PET scans were correctly classified. Increasing BTV was associated with shorter OS (P < 0.0001).Conclusion. A 20-minute F-18-FET PET scan is a powerful tool to distinguish posttreatment changes from recurrent glioblastoma 6-month postradiotherapy, and predicts OS.