Late radiation-induced contrast enhancing brain lesions (CEBL) on MR images after proton therapy of brain tumors have been observed to occur frequently in regions of high linear energy transfer (LET) and in proximity to the ventricular system. Published in the Red Journal, the Heidelberg study analyzed 110 low-grade glioma patients treated with proton therapy to determine if the risk for CEBLs is increased in proximity to the ventricular system and if there is a relationship between relative biological effectiveness (RBE) and LET. Out of 110 patients, 23 exhibited one or several CEBLs on follow-up MR images.

This study also presented a voxel-level model that predicts the localization of late MRI contrast change and extrapolate a patient-level model that allows treatment-plan based risk prediction. The findings of this study present clinical evidence for an increased risk in ventricular proximity and for a proton RBE that increases significantly with increasing LET.