Evaluation of the electron energy fluence and angular distributions from a clinical accelerator. A BEAMnrc Monte Carlo study

Understanding of the incident electron
energy and angular distributions from clinical
electron accelerators (linacs) is important for
dosimetry and treatment planning. The most
important goals of this study were to evaluate the
energy fluence and angular distributions of electron
beams from a Neptun 10PC linac using the Monte
Carlo (MC) code. Materials and Methods: The linac
electron beams (6, 8, and 10 MeV) were modeled,
using the BEAMnrc MC system based on the Electron-
Gamma-Shower (EGSnrc) code. Central axis depthdose
curves and dose profiles of the electron beams
were measured experimentally, and calculated with
the MC for three field sizes. In order to benchmarking
the simulated models, the calculated and measured
dose distributions were compared with Kolmogorov–
Smirnov (KS) statistical test. Results: The KS test
indicated that the calculated percent depth dose
(PDD) and dose profile values for the three electron
beam energies well agree with measured data (within
2% everywhere). The results also showed good
agreement (discrepancies smaller than 1%) between
the simulated electron energy parameters and those
calculated from energy-range relationships using
equations for the reference field size. Conclusion: The
results showed that there was no significant
difference between energy fluence curves of each
electron beam energy at different field sizes. In
addition, the results of the calculated angular
distributions showed that the direction of the electron
emerged from the treatment head and trimmer
applicators were in forward direction