Optimisation of field flatness and depth-dose for therapy electron beams.

Curves relating beam energy, scattering foil thickness, central-axis depth-dose, and beam flatness have been generated using data taken on a Siemens 200A betatron. The curve set allows a single combination of tungsten foil thickness and electron beam energy to be chosen that will provide the optimum depth-dose distribution and sufficient field flatness for any specific clinical requirement.