This study aims to assess the feasibility of a novel Beryllium Oxide (BeO) based ceramics to be used as optically stimulated luminescence (OSL) dosimeters for monitoring of high-energy beams used in radiotherapy. The BeO ceramic dosimeters doped with alkali and rare earth metals (BeO:Na5%,Ce0.005%,Tb0.05%, BeO:Na5%,Ce0.01%,Er0.01%, and BeO:Na5%,Ce0.01%,Dy0.01%) were fabricated in pellet forms, and their luminescence responses were measured at the virtual water phantom interfaces for various field sizes of a 6 MV flattening filter-free photon beam of Varian LINAC. The OSL dosimeter's performance has been confirmed their practical usefulness as in vivo dosimeters in radiotherapy clinics. The provided dose estimates were validated using varying X-ray energies and doses, typically employed for actual medical radiotherapy systems. Our results indicated that the studied dosimeters rendered an almost linear response in the dose range of 0.05 Gy–20 Gy delivered from the 6 MV X-ray beam. Fading of the stored OSL was found to be less than 5% after a short storage period. The dependencies of OSL responses concerning beam energy, dose rate, irradiation angle, depth, and field size are all found to be supportive of the successful utilization of the BeO OSLDs in clinical environments.