Nanoparticle-mediated radiation therapy (NPRT) is an emerging modality for radiosensitization of highly resistant cancers such as brain cancers. This is due to the ability of specific nanoparticles (NPs) to increase physical dose deposition and subsequent direct damage to cells and DNA within their local vicinity, through enhanced generation of reactive oxygen species, ROS. Here, we report the successful use of PEGylated (biocompatible) core-shell quantum dots (QDs) and carbon quantum dots (CQDs) to simultaneously enhance and assess ROS generation while radiosensitizing highly radioresistant brain cancer cell lines: T98G and U87 Glioblastoma cells. Relative peak fluorescence intensity ratio calculations and average intensity comparisons show highly significant (***p<0.001) enhancement of ROS generation, for 5 Gy and 20 Gy irradiation, applied using a Faxitron Cell Irradiator. By quantifying post-radiotherapy cell attachment, proliferation, migration, cell survival and cell death using electric cell-substrate impedance sensing and clonogenic assays, we demonstrate potentially improved in vitro radiotherapeutic outcomes for brain cancer cells radiosensitized using PEGylated CdSe/ZnS QDs and CQDs.