title: Comparison of film measurements and Monte Carlo simulations of dose delivered with very high-energy electron beams in a polystyrene phantom.
abstract: OBJECTIVE
  To measure radiation dose in a water-equivalent medium from very high-energy electron (VHEE) beams and make comparisons to Monte Carlo (MC) simulation results.
  
  
  METHODS
  Dose in a polystyrene phantom delivered by an experimental VHEE beam line was measured with Gafchromic films for three 50 MeV and two 70 MeV Gaussian beams of 4.0-6.9 mm FWHM and compared to corresponding MC-simulated dose distributions. MC dose in the polystyrene phantom was calculated with the EGSnrc/BEAMnrc and DOSXYZnrc codes based on the experimental setup. Additionally, the effect of 2% beam energy measurement uncertainty and possible non-zero beam angular spread on MC dose distributions was evaluated.
  
  
  RESULTS
  MC simulated percentage depth dose (PDD) curves agreed with measurements within 4% for all beam sizes at both 50 and 70 MeV VHEE beams. Central axis PDD at 8 cm depth ranged from 14% to 19% for the 5.4-6.9 mm 50 MeV beams and it ranged from 14% to 18% for the 4.0-4.5 mm 70 MeV beams. MC simulated relative beam profiles of regularly shaped Gaussian beams evaluated at depths of 0.64 to 7.46 cm agreed with measurements to within 5%. A 2% beam energy uncertainty and 0.286° beam angular spread corresponded to a maximum 3.0% and 3.8% difference in depth dose curves of the 50 and 70 MeV electron beams, respectively. Absolute dose differences between MC simulations and film measurements of regularly shaped Gaussian beams were between 10% and 42%.
  
  
  CONCLUSIONS
  The authors demonstrate that relative dose distributions for VHEE beams of 50-70 MeV can be measured with Gafchromic films and modeled with Monte Carlo simulations to an accuracy of 5%. The reported absolute dose differences likely caused by imperfect beam steering and subsequent charge loss revealed the importance of accurate VHEE beam control and diagnostics.
authors.affiliation: Department of Radiation Oncology, Stanford University, Stanford, California 94305-5847.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Bazalova-Carter
authors.affiliation: Department of Radiation Oncology, Stanford University, Stanford, California 94305-5847.
authors.forename: Michael
authors.initials: M
authors.lastname: Liu
authors.affiliation: Department of Radiation Oncology, Stanford University, Stanford, California 94305-5847.
authors.forename: Bianey
authors.initials: B
authors.lastname: Palma
authors.affiliation: SLAC National Accelerator Laboratory, Menlo Park, California 94025.
authors.forename: Michael
authors.initials: M
authors.lastname: Dunning
authors.affiliation: SLAC National Accelerator Laboratory, Menlo Park, California 94025.
authors.forename: Doug
authors.initials: D
authors.lastname: McCormick
authors.affiliation: SLAC National Accelerator Laboratory, Menlo Park, California 94025.
authors.forename: Erik
authors.initials: E
authors.lastname: Hemsing
authors.affiliation: SLAC National Accelerator Laboratory, Menlo Park, California 94025.
authors.forename: Janice
authors.initials: J
authors.lastname: Nelson
authors.affiliation: SLAC National Accelerator Laboratory, Menlo Park, California 94025.
authors.forename: Keith
authors.initials: K
authors.lastname: Jobe
authors.affiliation: SLAC National Accelerator Laboratory, Menlo Park, California 94025.
authors.forename: Eric
authors.initials: E
authors.lastname: Colby
authors.affiliation: Department of Radiation Oncology, Stanford University, Stanford, California 94305-5847.
authors.forename: Albert C
authors.initials: AC
authors.lastname: Koong
authors.affiliation: SLAC National Accelerator Laboratory, Menlo Park, California 94025.
authors.forename: Sami
authors.initials: S
authors.lastname: Tantawi
authors.affiliation: SLAC National Accelerator Laboratory, Menlo Park, California 94025.
authors.forename: Valery
authors.initials: V
authors.lastname: Dolgashev
authors.affiliation: Department of Radiation Oncology, Stanford University, Stanford, California 94305-5847.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Maxim
authors.affiliation: Department of Radiation Oncology, Stanford University, Stanford, California 94305-5847.
authors.forename: Billy W
authors.initials: BW
authors.lastname: Loo
mesh_terms: D003198:Computer Simulation; D004583:Electrons; D005373:Film Dosimetry; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011137:Polystyrenes; D011829:Radiation Dosage; D035501:Uncertainty; D014867:Water
chemical_list: D011137:Polystyrenes; D014867:Water