This study is testing a new cancer drug called **AZD1390** with radiation therapy for kids who have certain brain tumors, like high-grade glioma. AZD1390 is a **kinase inhibitor** which helps stop cancer cells from growing. The study aims to find the best dose and see how well it works with radiation therapy. Radiation therapy uses high energy to kill cancer cells and shrink tumors. Patients will take AZD1390 by mouth and receive radiation over about 6 weeks. After that, they continue using AZD1390 for a short period if there are no bad side effects.

• The study will last up to 5 years with frequent follow-ups, especially in the first two years.
• Participants must be between 1 and 22 years old, and not have had certain treatments before.
• There might be risks from side effects, but medical checks will monitor safety.