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. 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

Comparison of MCNP4C, 4B and 4A Monte Carlo codes when calculating electron therapy depth doses

Monte Carlo simulation of radiation transport is considered to be one of the most accurate methods of radiation therapy dose calculation. There are different Monte Carlo codes for simulation of photons, electrons and the coupled transport of electrons and photons. MCNP is a general purpose Monte Carlo code that can be used for electron, photon and coupled photon-electron transport. In this study the MCNP4A, 4B and 4C have been compared when calculating electron beam doses in water. For simulating, the geometry and other parameters were the same for three codes. By choosing two energy indexing algorithm [ITS and MCNP], absorbed doses were scored in water. 10[6] Particles were followed in these three cases. MCNP4C and 4B gave different results compared to 4A when the ITS algorithm was used in 4B and 4C versions. There was a good agreement between versions 4B and 4C. For the energy spectrum, there were significant differences between these three versions in two planes. Because of new improvements in electron transport in 4C, this version is reliable for electron transport and also requires a shorter time than the two previous versions. These results, in addition to the practical measurements acquired with MCNP4B by other investigators, suggest that in electron transport the user should use the ITS indexing energy algorithm