Validation of a Lévy electron energy straggling model for an Elekta Synergy® linear accelerator

In this study, an EGSnrc based Monte Carlo electron model was validated for an Elekta Synergy® 160-leaf Agility™ linear accelerator. A previously reported electron energy straggling model based on a Lévy distribution was tested against water tank measurements and a specially designed heterogeneous multi-layered phantom. This included PDD, beam profile, and relative output factor (ROF) comparison. All data passed a 2%/2 mm gamma criterion with the exception of some ROF data, which showed discrepancies of up to 2.7%.

BEAMnrc was used to accurately model the linac that included the improved exit electron energy spectrum based on a Lévy distribution. The resulting BEAMnrc phase space files were used as sources in DOSXYZnrc for water tank dose distribution simulations consisting of 6 electron beam energies, 11 field sizes, and source-to-surface distances (SSDs) of 95 and 100 cm. Evaluation parameters included PDD, dose profiles, and relative output factors, as well as phantom PDD and dose profile measurements with EBT3 gafchromic film.

The improved exit electron beam energy spectrum caused simulated data to comply with measured data (PPD's and dose profiles) with a 100% pass rate using a 2%/2 mm criterion except for some relative output factors that deviated by 2.7% from measured ones in water. This was observed for both 95 and 100 cm SSD data. Good agreement was obtained between film and simulation data within 2% in more than 90% of PDD and profile measurements.

The Lévy based energy straggling model for electron beams allowed for accurate electron beam characterization in water tank and phantom measurements.