The use of electronic brachytherapy (EB) has grown rapidly over the past decade, and is gaining significant interest from the global medical community as an improved user-friendly technology. However, the present EB machines all use electron beams at energies of 100 kV or less to generate the X-ray photons, which limits their use to low dose-rate brachytherapy. In this proposal, Euclid Beamlabs focuses on the development of an ultra-compact and light weight 1- MeV electron source to generate and deliver >250 kV X-ray photons to the patient. The device is intended to retrofit to existing brachytherapy applicators. Our proposed accelerating structure is a dielectric-based accelerator. Because of the use of high permittivity dielectrics, the transverse size of the cavity is significantly reduced, becoming comparable to the thickness of a pencil. With the help of optimized focusing elements, the beam will be transported through a 1~2-mm diameter pipe to the Bremsstrahlung radiation target, thus delivering the dose in a highly localized regime. The dimension of the pipe will be chosen for compatibility with existing brachytherapy applicators. In Phase I, we will develop a fully functioning prototype and measure its critical parameters, including the delivered electron and photon energies, the dose rate, etc. The Technical Readiness Level (TRL) of the developed technology will reach TRL4 (feasibility proved) upon the completion of Phase I.