Extending the general field equation to fit the dose distributions of a variety of therapy units.

Abstract The general field equation was originally developed for the Eldorado A therapy unit and was easily extended to other similar cobalt units. Attempts to fit the general field equation to dose data for more recent cobalt units or other energy sources have resulted in less accurate dose determinations. While there is nothing to prevent the use of a different equation for each type of therapy unit, it is obviously simpler to have a single equation with only the coefficients being different for each unit, provided the equation does not become too complicated. In this paper we derive a single equation which is able to represent satisfactorily the dose distribution of the following therapy units: Theratron F, Theratron 80 or Eldorado 8, Gammatron 3, Picker C8, Picker C9, Varian 6, and a 22 MeV betatron.