An evaluation of epoxy resin phantom materials for electron dosimetry.
The use of epoxy resin 'solid water' (water substitute) phantoms is becoming increasingly common in radiotherapy dosimetry, and depth ionization curves and conversion factors from ionization to dose identical to water have often been assumed. Fluence ratios of water to solid water for WTe (produced by Radiation Physics, St Bartholomew's Hospital, London) and RMI 457 (produced by Radiation Measurements Inc., Middleton, Wisconsin) have therefore been determined and have been found to decrease with energy, which, within measurement uncertainty, can be described with a linear function dependent on mean electron beam energy at the depth of measurement, Ed. The fluence ratios for WTe are very close to unity (i.e. within the measuring uncertainty) for most of the energies examined, the exception being a nominal 20 MeV beam. The results also show that an assumption of unity for the fluence ratios of RMI 457 may introduce a systematic error of the order of 1% in electron beam dosimetry at lower energies. As regards the depth ionization curves measured in the respective solid water materials, these are shown to be in agreement with those measured in water within the limits of the measuring uncertainty.
Nisbet
A
A
Department of Medical Physics and Medical Engineering, University of Edinburgh, Western General Hospital, UK.
Thwaites
D I
DI
D055592:Biophysical Phenomena; D001703:Biophysics; D004583:Electrons / Q000627:therapeutic use*; D004853:Epoxy Resins; D006801:Humans; D019047:Phantoms, Imaging; D011874:Radiometry / Q000295:instrumentation* / Q000706:statistics & numerical data; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy; D013679:Technology, Radiologic; D014867:Water
D004853:Epoxy Resins; D014867:Water