Abstract AIM Not uncommonly, we come across significantly large high grade glioma cases (HGGs). With standard delineation protocols, we end up irradiating a large volume of normal brain. Emami & QUANTEC data define normal brain tolerance doses, however they are often of limited use in clinic practice. Thus, we reviewed our patients with significant tumor volumes to derive a safe dose/ volume level for brain. METHODOLOGY Patients with HGGs over the last 3 years were extracted from Mosaiq™ information system. The output was sorted with respect to clinical target volumes from lowest to highest. The top 25 percentile i.e. patients with a CTV of > 412cc (n=53) were identified for this study. Data was collected with respect to clinical, tumor characteristics and radiotherapy parameters. RESULTS Median age of population was 53 and majority (n=38) were males. Nine patients had multi-focal tumors while six had bilateral extension. Majority of the study group had Glioblastoma Multiforme (n=44), whereas 6 had Grade 3 tumors. Most of the patients could only have a biopsy (n=27). Molecular profile showed 42 were Isocitrate-Dehydrogenase negative and 26 were unmethylated tumors. Stupp’s & Perry’s regimen were the commonly used protocols, however patients (n=7) with significant volumes near critical structures were treated with doses in the range of 50.4 – 55Gy in 30 fractions. The CTV volumes in the population ranged from 412 – 1223 cc while total brain volume range was 1112 – 1667 cc. Median of 43.5% of brain volume was covered in the PTV, while median of 5% of brain volume outside the PTV was treated to BED2 of 100Gy. Median survival was 12.4 months. CONCLUSION Our study shows reasonable tolerance of radiotherapy doses of > 50 Gy to larger volumes of brain. We propose a multi-center collaborative study to derive a new standardized dose volume tolerance.