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Background. The current method for assessing progressive disease (PD) in glioblastoma is according to the Response Assessment in Neuro-Oncology (RANO) criteria. Bevacizumab-treated patients may show pseudoresponse on postcontrast T1-weighted (T1w) MRI, and a more infltrative non-enhancing growth pattern on T2w/?uid attenuated inversion recovery (FLAIR) images. We investigated whether the RANO criteria remain the method of choice for assessing bevacizumab-treated recurrent glioblastoma when compared with various volumetric methods. Methods. Patients with assessable MRI data from the BELOB trial (n = 148) were included. Patients were treated with bevacizumab, lomustine, or both. At frst and second radiological follow-up (6 and 12 wk), PD was determined using the 2D RANO criteria and various volumetric methods based on enhancing tumor only and enhancing plus non-enhancing tumor. Differences in overall survival (OS) between PD and non-PD patients were assessed with the log-rank test and a Cox model. Hazard ratios (HRs) and their 95% CIs were determined. Results. For all patients together, all methods (except subtraction of non-enhancing from enhancing volume at frst follow-up) showed signifcant differences in OS between PD and non-PD patients (P <.001). The largest risk increase for death in case of PD at both frst and second follow-up was found with the RANO criteria: HR = 2.81 (95% CI, 1.92-4.10) and HR = 2.80 (95% CI, 1.75-4.49), respectively. In the bevacizumab-treated patients, all methods assessed showed signifcant differences in OS between PD and non-PD patients. There were no signifcant differences between methods. Conclusions. In the frst 12 weeks, volumetric methods did not provide signifcant improvement over the RANO criteria as a posttreatment prognostic marker.