The purpose of this investigation is to measure the total attenuation coefficients (TACs) of plaster materials using different geometries of the plaster, field sizes, and photon beam energies. The percent depth dose measurements were made using X-rays at 6 MV and 18 MV from the linear accelerator in order to plan the probable radiation dose to be given to the patient wearing a plaster cast. The TAC was experimentally determined in solid phantoms of various thicknesses both with and without plaster over areas of 5 x 5 cm (2), 10 x 10 cm(2), and 15 x 15 cm(2). The experimentally measured TAC for plaster was compared to that of the NIST program. The TAC of solid phantom with plaster was found to be larger than without plaster. This means that d(max) is very close to the skin and that in these situations plaster has a bolus effect, increasing the skin's dose.