A method of estimating bremsstrahlung scattering from a body-sized phantom was developed for quanta of energy up to 10 mev. The method is based on the experiments of W. R. Dixon, et al., with the scattering of Co-60 rays and on the calculation of single Compton scattering by means of the Klein-Nishina formula. By a partly theoretical and partly empirical method the single scattering calculations were combined with the total scattering of Co-60 gamma rays measured by Dixon et al., to give a safe, conservative estimate of total scattering from the phantom up to 10 mev. These safe estimates together with the inverse square law and the concrete attenuation curves of the U. S. National Bureau of Standards made it possible to determine the proper protective wall thickness in the angular range from 18[degree] to 180[degree]. Protective wall thickness thus calculated, has been successfully applied in the design of the room housing the 6 mev linear accelerator at Stanford Hospital.