Determination of three parameters describing the uncollimated electron beam in air

The parameters that describe the electron dose distribution phi (r, theta, z) produced in air by an uncollimated clinical electron beam are accurately determined. For the determination of these parameters the multiple scattering theory of Fermi is assumed. A new method which determines the angular variance at the phantom surface is introduced and the results appear to be in good agreement with the multiple scattering theory. Knowledge of the values of these parameters is essential for a numerical determination of the dose distribution in air and in the patient.