**2. Experimental Section**

We performed a retrospective analysis of patients treated in our clinic between 2016 and 2019 to identify patients with cerebral radiation necrosis who received bevacizumab and who had at least one documented cortisol value. AI was defined by our laboratory when morning (8–10 a.m.) serum cortisol levels were below 7.25 μg/dL (200 nmol/L) [19]. Cerebral radiation necrosis was diagnosed based on the localization of a lesion within a previously irradiated region, compatible MRI findings including no significant increase in perfusion, non-solid morphology, if available no significantly increased metabolism in O-(2-(18F)fluoroethyl)-L-tyrosine (18F-FET) positron emission tomography (PET) as well as follow-up scans compatible with the diagnosis of radiation necrosis. The patient collective was evaluated with regard to histology, patient age at tumour diagnosis, patient age at cortisol analysis, duration and maximum dose of dexamethasone, the need for hydrocortisone substitution, as well as the radiologic response to bevacizumab treatment. MRI scans including axial fluid-attenuated inversion recovery (FLAIR), T2 weighted, and T1 weighted images before and after application of gadolinium-based contrast agent were analysed by an experienced, board-certified neuroradiologist (M.W.). The extent of edema was estimated on the axial FLAIR or T2 weighted sequence. Response to bevacizumab treatment was defined as a reduction of the edema by at least 25% [18]. Additionally, intracranial contrast-enhancing lesions were measured on postcontrast images as a further marker of the disruption of the blood–brain barrier. Partial response was defined as a reduction of contrast enhancement by at least 50%, and complete response by complete absence of contrast enhancement. Progressive disease was defined as an increase of at least 25%.

Statistical analysis: SPSS Statistics Version 22 was used for statistical analysis (IBM, Armonk, NY, United States). Ethics approval was obtained from the ethics committee of the University Hospital Frankfurt; Goethe University (SNO\_01-08). This study was performed in accordance with the declaration of Helsinki.

## **3. Results**
