A 3-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 lead s to six parameters, with which S-p(r) is described as a smooth functi on of the field radius r for beam qualities in the range from Co-60 up to 25 MV. The parameters allow S-p values to be calculated at interme diate beam energies and for any field shape. Calculated S-p(X, Y) valu es for rectangular fields (X, Y) can be subsequently used as reference values to compare with measured S-p(X, Y) values, for example when ap praising a new beam.