Radiation therapy remains one of the more widely used cancer treatment, as it comprisesthe standard of care for more than 50% of cancer patients. However, this therapeutic modalityremains limited by an intrinsic toxicity caused by a lack of contrast between the dose depositedin the cancer tissue and the dose deposited in the surrounding healthy tissue.This limitation has particular relevance to glioblastoma, one of the most common typesof brain cancers in adults. Radiation therapy for glioblastoma is challenged by the presenceof sensitive surrounding tissues, which strongly limits the radiation doses that can safely bedelivered. Consequently, glioblastoma has a dismal prognosis: the median survival is approx-imately one year, despite the current standard of care.To improve the efficacy of radiation therapy, scintillating nanoparticles are emerging aspromising therapeutic agents. These nanoscintillators can act as both contrast enhancers forradiation therapy, while also functioning as a local light source to enable deep tissue photody-namic therapy to induce an additional, localized cytotoxic effect.To investigate this innovative concept in a physicochemical and biomedical context, weexplore the use of LaF3and LaF3:Ce nanoparticles to achieve radiation dose enhancement in3D models of glioblastoma using monochromatic synchrotron radiation