In this project, we want to study the FLASH effect in a preclinical paediatric mouse model of DIPG, using an irradiation setting very similar to the standard radiotherapy course for human DIPG (treatment fractionated over 3 weeks). We will irradiate juvenile mice (3 weeks old) with DIPG tumours (implanted), with both conventional (= low beam current) and FLASH (= high beam current). We will observe the tumour regression (or eventual progression) as well as measure their cognitive performance. To disentangle the impact of the tumour on the cognitive performance, we will also perform a control irradiation with the same condition in healthy juvenile mice. Our aim is to show that the FLASH effect enhances the therapeutic outcome in DIPG, by reducing side effects related to radiotherapy delivered to a developing brain, and provide the preclinical data needed for a future FLASH proton therapy pilot trial in DIPG patients at the Centre for Proton Therapy.