During certain treatment using an electron beam, internal shielding using high atomic number material is used. But this high atomic number material as an internal shielding causes unnecessarily high dose to the tissue right above the internal shielding by the electron backscattering effect. This study shows the amount of the unnecessary dose delivered by the electron backscattering and the effectiveness of the Bayer-dental as a mold for fabricating internal shielding made with cerrobend.