title: A semi-analytical model for calculating the penetration depth of a high energy electron beam in a water phantom with a magnetic field.
abstract: OBJECTIVE
  As an electron beam is incident on a uniform water phantom in the presence of a lateral magnetic field, the depth-dose distribution of the electron beam changes significantly and forms the well-known 'Bragg peak', with a depth-dose distribution similar to that of heavy ions. This phenomenon has pioneered a new field in the clinical application of electron beams. For such clinical applications, evaluating the penetration depth of electron beams quickly and accurately is the critical problem.
  
  
  METHODS
  This paper describes a model for calculating the penetration depth of an electron beam rapidly and correctly in a water phantom under the influence of a magnetic field. The model was used to calculate the penetration depths under different conditions: the energies of electron beams of 6, 8, 12 and 15 MeV and the magnetic induction intensities of 0.75, 1.0, 1.5, 2.0 and 3.0 T. In addition, the calculation results were compared with the results of a Monte Carlo simulation.
  
  
  RESULTS
  The comparison results indicate that the difference between the two calculation methods was less than 0.5 cm. Moreover, the computing time of the calculation model was less than a second.
  
  
  CONCLUSIONS
  The semi-analytical model proposed in the present study enables the penetration depth of the electron beam in the presence of a magnetic field to be obtained with a computational efficiency higher than that of the Monte Carlo approach; thus, the proposed model has high potential for application.
authors.affiliation: Key Laboratory for Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610065, China.
authors.forename: Shihu
authors.initials: S
authors.lastname: You
authors.affiliation: Key Laboratory for Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610065, China. Electronic address: ChengJ.Gou@263.net.
authors.forename: Chengjun
authors.initials: C
authors.lastname: Gou
authors.affiliation: Key Laboratory for Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610065, China.
authors.forename: Zhangwen
authors.initials: Z
authors.lastname: Wu
authors.affiliation: Key Laboratory for Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610065, China.
authors.forename: Qing
authors.initials: Q
authors.lastname: Hou
mesh_terms: D004583:Electrons / Q000627:therapeutic use*; D060526:Magnetic Fields; D008962:Models, Theoretical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D013499:Surface Properties; D014867:Water
chemical_list: D014867:Water
keywords: Electron beam; Magnetic field; Monte Carlo; Radiotherapy