This is a prospective, open-label, multicentric study designed to correlate the dose delivered to the hippocampus with declarative memory deficits 2 years after radiotherapy treatment in a paediatric population who had received brain irradiation between the ages of 4 and 12 for a brain tumour. In order to meet this objective, several neuropsychological assessments consisting of parental questionnaires and cognitive tests will be carried out during the course of the study, at the following two stages: * A 1st assessment at patient inclusion, i.e. 2 years after the end of radiotherapy treatment, * And a second assessment 2 years after patient inclusion, i.e. 4 years after the end of radiotherapy treatment. A retrospective assessment of the patient's neurocognitive level 1 year before the diagnosis of the disease will also be carried out at inclusion, with the parents completing a questionnaire specifically designed for the trial. In addition, patients who have received their radiotherapy treatment at the IUCT-O will be offered participation in the ancillary imaging study. If the parents and the patient agree, multimodal MRI scans specific to the study (without injection of contrast) will be performed at inclusion and 2 years after inclusion. Imaging and radiotherapy data will be collected in parallel using the PediaRT software used in current practice (collection of radiotherapy dosimetric data as well as standard MRI examinations pre-operatively, post-operatively, and at the 2-year and 4-year follow-up). 130 patients will be included in this study.