Abstract
An annular secondary scatterer intercepts electrons outside the useful field and redirects some of them into a distribution which complements that from the primary scatterer, producing flattened electron therapy fields with good source geometry and a minimum of scattered thickness. Actual beam profiles were compared with a mathematical model of the multiple scattering geometry to determine the electron energies and field sizes at which other phenomena such as air scattering at low energies and X-ray contamination at high energies become significant.