In radiation oncology, while radiation is effective in killing cancer cells, the dose safely deliverable to the target volume is often limited by the possibility of collateral damage to surrounding healthy tissues. However, for some cancer sites, it has been shown that a dose escalation in the tumor could significantly improve local control and patient survival [1]. While recently developed methods such as intensity-modulated radiation therapy, volumetric-modulated arc therapy and imageguided radiation therapy have improved the delivered radiation dose conformality, dose escalation remains an important clinical challenge that needs to be addressed to improve the efficacy of radiation therapy [2]. Nanoparticles design is a rising landscape in the era of modern oncology offering new perspectives. The enhancement of radiation effect induced by radiosensitizing nanoparticles is probably one of the most translational aspects. Radiosensitizing nanoparticles increase the radiobiological effects within the site of disease while maintaining the current clinical constraints on dose delivered to healthy organs. The photoelectric interaction increases strongly as a function of the atomic number of the nanoparticle (proportional to Z–Z), giving these particles a high interaction probability with low-energy photons and allowing the formation of additional diffused photons, photoelectrons, Auger electrons and reactive oxygen species that have the potential to amplify the biological damage. Even under high-energy photon irradiation, highZ nanoparticles can interact with primary or secondary species permitting a highly efficient nanoscale dose deposition around the nanoparticle [3]. Consequently, the differential effect between healthy tissue and tumor tissue is improved. The efficacy of nanoparticles as radiosensitizers has been demonstrated at the preclinical level for multiple high-Z nanoparticles since Hainfeld et al. demonstrated the potential of gold nanoparticles after systemic injection [4], and at the clinical level for hafnium nanoparticles [5]. However, because of the injection method (intratumoral injection) and because of their size (50 nm), the hafnium nanoparticle applications are mainly limited to easyto-access tumor sites, such as sarcoma, head and neck and prostate cancers. For the majority of other cancer sites, intravenous injection remains an obligation. To address these limitations while still ensuring low toxicity to the healthy tissues, thera nostic nanoparticles were created, combining diagnostic and therapeutic properties. Gadolinium is the most well-known element for biomedical applications. Its use in medicine is directly correlated with the development of contrast agents for MRI, a noninvasive and nonionizing method for acquiring volumetric images with high spatial resolution and excellent soft-tissue contrast. Some clinics have begun to replace CT simulation with MRI simulation for radiation treatment Pushing radiation therapy limitations with theranostic nanoparticles