A three-Gaussian fit of phantom scatter correction data

The phantom scatter correction factor S(p), of megavoltage photon beams can be accurately described using a three-Gaussian fit. The model leads to six parameters, with which S(p),(r) is described as a smooth function of the field radius r for beam qualities in the range from ⁶⁰Co up to 25 MV. The parameters allow S(p), values to be calculated at intermediate beam energies and for any field shape. Calculated S(p)(X, Y) values for rectangular fields (X, Y) can be subsequently used as reference values to compare with measured S(p),(X, Y) values, for example when appraising a new beam.