ReRAD is a phase II single-arm, non-randomized study of re-irradiation of children with diffuse intrinsic pontine glioma (DIPG). The study seeks to determine the safety and effectiveness of a second course of radiation therapy (re-irradiation; rRT). The hypothesis is that the use of rRT will be feasible, safe and effective in prolonging life. The primary objective of the study is to estimate the length of secondary progression-free survival (PFS-2) and the overall survival (OS) of patients with progressive or recurrent DIPG who are treated with re-irradiation.