Improved simulation of small electron fields for external beam radiation therapy

Abstract

This paper reports on improved simulation of small electron fields from a Siemens Primus linear accelerator. Accelerator simulation was performed using the Monte Carlo user code BEAMnrc. Source and geometry parameters used were obtained from previous measurements and simulation of the linear accelerator with maximum electron field size (40 x 40 cm2). Careful measurements of electron dose distributions were performed for fields ranging from an open 25 x 25 cm2 electron applicator to a 10 x 10 cm2 applicator containing a 1 cm diameter cerrobend insert. Monte Carlo calculated and measured data generally matched to within 2 % or 1 mm. This study has used improved source and treatment head simulation parameters and exacting measurements to closely match measured and simulated dose distributions for small electron fields.