Paediatric H3K27/H3G34 mutant diffuse midline gliomas are high grade gliomas that arise in midline structures/cerebral hemispheres and are known to have dismal outcomes. Standard treatment includes definitive radiation therapy to primary site along with concurrent temozolomide chemotherapy following histological confirmation with a biopsy. Studies have shown poorer outcomes in the paediatric age group compared to that of adults and an increased risk to fail/recur in the leptomeninges(covering of brain and spinal cord). The following study is planned in order to assess the benefit of craniospinal irradiation(delivering radiotherapy to brain, spinal cord and its covering membrane in this high risk population. Thereby the investigator aim to improve survival in newly diagnosed histone mutant pediatric midline gliomas in the upfront setting. Patterns of disease failure, treatment related toxicities and quality of life will also be assessed as a part of this study. If proven beneficial, this study will influence how patients with this diagnosis will be treated in the future.