A sector-integration method for calculating the output factors of irregularly shaped electron fields

An empirical model is presented that uses a sector-integration method for calculating the output factors of irregularly shaped electron fields. The sector-integration method accounts for changes in electron fluence, lateral scatter equilibrium, and scatter from the edge of a cutout shield. This method is tested for elliptical and rectangular fields with a ratio of the long-to-short axis as great as 4 to 1. Differences between measured and calculated values for output factors were less than +/- 1%. Comparisons were also carried out for a large number of cutout shields that were used in the clinic and similar levels of accuracy were obtained. (C) 1997 American Association of Physicists in Medicine.