A semi-empirical method for calculating the effect of air gap space on output factors on electron beam dose distributions.

Abstract

A simple approach to calculate the effect of air gap on output factors on electron beam dose distribution is presented. The method accounts for variations of pencil beam parameters using a model developed by Bruinvis et al. [4,5]. The evaluation of this method is based on measurements of the output factors at various distances between the final collimating device and the phantom surface. Comparison of calculations and measurements of output factors for various cone sizes and 0, 2 and 4 cm air gaps show agreement to within approximately 1.5% for electron energies of 6-13.5 MeV and field sizes of 5.3-10 cm in diameter. The accuracy of this semi-empirical method can be considered clinically acceptable and reduces the amount of experimental work needed.