title: Field size dependence of effective source distance and field factors of a 9 MeV electron beam.
abstract: Effective source distances and field factors were measured for a number of square and rectangular fields using a 9 MeV electron beam from a Varian 2100-C linear accelerator. Mathematical relationships between effective source distance and field size, and field factor and field size were derived. For 9 MeV electrons, effective source distance is dependent on the field area and applicator cone, while field factors are dependent on the elongation of the field, the field area and applicator cone. Measured field factor data for rectangular fields were compared to field factors obtained using the "square root" method and found to agree to within 0.5%. In some instances, field factors can vary up to 10% for the same field size in different electron applicator cones.
authors.affiliation: Department of Medical Physics and Bioengineering, Christchurch Hospital, New Zealand.
authors.forename: S P
authors.initials: SP
authors.lastname: Baggarley
authors.forename: D M
authors.initials: DM
authors.lastname: Mannering
authors.forename: R P
authors.initials: RP
authors.lastname: Hugtenburg
authors.forename: J R
authors.initials: JR
authors.lastname: Turner
mesh_terms: D004583:Electrons; D008961:Models, Structural; D010315:Particle Accelerators; D011874:Radiometry / Q000379:methods*; D011882:Radiotherapy, High-Energy; D012542:Scattering, Radiation