title: Water equivalence evaluation of PRESAGE(®) formulations for megavoltage electron beams: a Monte Carlo study.
abstract: To investigate the radiological water equivalency of three different formulations of the radiochromic, polyurethane based dosimeter PRESAGE(®) for three dimensional (3D) dosimetry of electron beams. The EGSnrc/BEAMnrc Monte Carlo package was used to model 6-20 MeV electron beams and calculate the corresponding doses delivered in the three different PRESAGE(®) formulations and water. The depth of 50 % dose and practical range of electron beams were determined from the depth dose calculations and scaling factors were calculated for these electron beams. In the buildup region, a 1.0 % difference in dose was found for all PRESAGE(®) formulations relative to water for 6 and 9 MeV electron beams while the difference was negligible for the higher energy electron beams. Beyond the buildup region (at a depth range of 22-26 mm for the 6 MeV beam and 38 mm for the 9 MeV beam), the discrepancy from water was found to be 5.0 % for the PRESAGE(®) formulations with lower halogen content than the original formulation, which was found to have a discrepancy of up to 14 % relative to water. For a 16 MeV electron beam, the dose discrepancy from water increases and reaches about 7.0 % at 70 mm depth for the lower halogen content PRESAGE(®) formulations and 20 % at 66 mm depth for the original formulation. For the 20 MeV electron beam, the discrepancy drops to 6.0 % at 90 mm depth for the lower halogen content formulations and 18 % at 85 mm depth for the original formulation. For the lower halogen content PRESAGE(®), the depth of 50 % dose and practical range of electrons differ from water by up to 3.0 %, while the range of differences from water is between 6.5 and 8.0 % for the original PRESAGE(®) formulation. The water equivalent depth scaling factor required for the original formulation of PRESAGE(®) was determined to be 1.07-1.08, which is larger than that determined for the lower halogen content formulations (1.03) over the entire beam energy range of electrons. All three of the PRESAGE(®) formulations studied require a depth scaling factor to convert depth in PRESAGE(®) to water equivalent depth for megavoltage electron beam dosimetry. Compared to the original PRESAGE(®) formulation, the lower halogen content formulations require a significantly smaller scaling factor and are thus recommended over the original PRESAGE(®) formulation for electron beam dosimetry.
authors.affiliation: Institute of Medical Physics, University of Sydney, Sydney, Australia.
authors.forename: Tina
authors.initials: T
authors.lastname: Gorjiara
authors.forename: Zdenka
authors.initials: Z
authors.lastname: Kuncic
authors.forename: Robin
authors.initials: R
authors.lastname: Hill
authors.forename: John
authors.initials: J
authors.lastname: Adamovics
authors.forename: Clive
authors.initials: C
authors.lastname: Baldock
mesh_terms: D003124:Colorimetry / Q000295:instrumentation* / Q000379:methods; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D009010:Monte Carlo Method; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy / Q000295:instrumentation* / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014867:Water
chemical_list: D014867:Water