Radiation-Induced Contrast Enhancement After Proton Therapy for Paediatric Brain Tumours: Association with Variable Relative Biological Effectiveness and Linear Energy Transfer

Background/Objectives: Proton therapy is widely used in paediatric neuro-oncology because of its favourable dose distribution and reduced exposure to radiation of healthy tissue. Nevertheless, current knowledge regarding radiation-induced contrast enhancements (RICE) is largely derived from adult proton therapy cohorts, while evidence in paediatric patients remains limited and the underlying biological mechanisms are still incompletely understood. This study investigated the incidence of RICE in paediatric patients with low-grade glioma (LGG) and ependymoma and evaluated potential associations with linear energy transfer (LET) and variable relative biological effectiveness (RBE)-weighted dose distributions.

Methods

In this retrospective single-centre study, paediatric patients with LGG or ependymoma were identified from a prospectively maintained institutional registry patients treated with proton therapy at the Heidelberg Ion-Beam Therapy Centre (HIT) between 2010 and 2024. Follow-up magnetic resonance imaging examinations were systematically reviewed for RICE. Lesions were contoured in RayStation and assessed dosimetrically using a fixed RBE of 1.1 and three variable RBE models. LET-weighted dose metrics and Dose(RBE) × LET products were compared between RICE regions and planning target volumes (PTVs). Overall survival and progression-free survival were estimated using Kaplan–Meier method.