This study is testing a new treatment for a type of brain cancer in children and young adults called **glioma**. Glioma is a fast-growing tumor that can occur in the brain or spine, and it is considered high-risk. A special kind of glioma called **DIPG** affects a part of the brainstem that helps control breathing and movement. The study looks at combining a drug called **selinexor** with radiation therapy to see if it can shrink these tumors. Selinexor is a medicine that blocks a protein helping cancer cells grow. The study will have two phases. First, researchers find the safest dose of selinexor. Then, they see how well it works to shrink tumors. Participants will take selinexor by mouth and receive radiation therapy over several weeks. They will have check-ups, including MRI scans for up to five years.

• **Study Length**: Up to 5 years of follow-up with treatment cycles lasting 28 days.
• **Visits Needed**: Regular visits for treatment and MRI scans.
• **Potential Risks**: Possible side effects from selinexor and radiation.