White polystyrene as a substitute for water in high energy photon dosimetry.
White polystyrene (C8H8 with 2 wt. % to TiO2) has been compared to water using photon beams with nominal accelerating potential of 4 MV, 6 MV, 15 MV and 25 MV. The absolute reading and hence the measured absorbed dose is found to be up to 3% lower in white polystyrene which can be taken into account by using a correction factor. From these data differences in relative measurements (TMR or percentage depth dose) can be calculated showing differences of less than 0.7% normalized to maximum dose. Since the correction factor shows a dependence on photon energy and field size the use of a common scaling factor is not possible. The effect on photon dosimetry is discussed.
Christ
G
G
Department of Medical Physics, University of Tübingen, Germany.
D055592:Biophysical Phenomena; D001703:Biophysics; D006801:Humans; D019047:Phantoms, Imaging; D017785:Photons; D011137:Polystyrenes; D011874:Radiometry / Q000379:methods* / Q000706:statistics & numerical data; D011880:Radiotherapy Planning, Computer-Assisted / Q000706:statistics & numerical data; D011882:Radiotherapy, High-Energy; D013679:Technology, Radiologic / Q000706:statistics & numerical data; D014867:Water
D011137:Polystyrenes; D014867:Water