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

ABSTRACT

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. 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. 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. 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