SU-E-T-269: The Evaluation of Copper as an Alternative for Cerrobend Electron Shielding

Purpose: To evaluate the replacement of Cerrobend by copper for electron beam cutouts. Methods: The dosimetric comparisons for circular copper‐and Cerrobend‐cutouts with diameters (1.0, 2.0, 3.0, 5.0, 7.5, 10.0, and 12.5 cm) were made using electron beams with energies (6, 9, 12, 16, and 20 MeV) from 3 Varian accelerators. A PTW Farmer chamber (0.125cc‐volume) was used for larger cutouts (diameters > 2cm), and an electron‐diode for the 2 smallest cutouts. Also a Markus parallel plate chamber was used. Results: (1) The tests showed little difference for the electron dosimetric characteristics, Eo, Eop, R50, Rp, and dmax. For larger cutout, the parameters were virtually the same for copper and Cerrobend. for smaller cutout (diameter = 3cm), small discrepancies were observed i.e. differences < 1mm for R50, Rp and dmax, =0.1MeV for Eop, and =0.3MeV for Eo. (2) The larger‐cutout outputs at dmax were also virtually the same (difference = 0.6%). For smaller cutouts (diameters = 3cm), the copper outputs were 2.0%∼5.0% higher than Cerrobend. (3) For lower energy electrons (