Benchmarking of Monte Carlo model of Siemens Oncor^® linear accelerator for 18MV photon beam: Determination of initial electron beam parameters

Abstract

OBJECTIVE: This study aims to benchmark a Monte Carlo (MC) model of the 18 MV photon beam produced by the Siemens Oncor® linac using the BEAMnrc and DOSXYZnrc codes. METHODS: By matching the percentage depth doses and beam profiles calculated by MC simulations with measurements, the initial electron beam parameters including electron energy, full width at half maximum (spatial FWHM), and mean angular spread were derived for the 10×10 cm2 and 20×20 cm2 field sizes. The MC model of the 18 MV photon beam was then validated against the measurements for different field sizes (5×5, 30×30 and 40×40 cm2) by gamma index analysis. RESULTS: The optimum values for electron energy, spatial FWHM and mean angular spread were 14.2 MeV, 0.08 cm and 0.8 degree, respectively. The MC simulations yielded the comparable measurement results of these optimum parameters. The gamma passing rates (with acceptance criteria of 1% /1 mm) for percentage depth doses were found to be 100% for all field sizes. For cross-line profiles, the gamma passing rates were 100%, 97%, 95%, 96% and 95% for 5×5, 10×10, 20×20, 30×30 and 40×40 cm2 field sizes, respectively. CONCLUSIONS: By validation of the MC model of Siemens Oncor® linac using various field sizes, it was found that both dose profiles of small and large field sizes were very sensitive to the changes in spatial FWHM and mean angular spread of the primary electron beam from the bending magnet. Hence, it is recommended that both small and large field sizes of the 18 MV photon beams should be considered in the Monte Carlo linac modeling.

Sensitivity Analysis of a 6 MeV Photon Beam Monte Carlo Model

“…Analytical dose calculation algorithms suffer from a clinically significant disagreement with measurement when treatment planning involves inhomogeneous areas. [ 1 ] These errors can become a dominant source of inaccuracy in treatment planning, especially in precision dose delivery techniques. Considering the uncertainties of dosimetry and treatment plan delivery, the importance of accurate dose calculations is highlighted.…”

“…However, the benchmarking process can become more targeted using sensitivity analysis of the calculated absorbed dose distributions to different parameters of linac and electron beam properties. [ 1 4 5 6 7 8 9 ]…”

The Study of Dosimetric Characteristics of the XHA600D Medical Linear Accelerator Based on a Monte Carlo Code

“…ese steps are ultimately designed to obtain the signi cant parameters in TPS model building. Many investigations have been conducted to benchmark the incident electrons of other medical linear accelerators such as Elekta [3][4][5], Varian [6][7][8][9], and Siemens [10,11], but no dosimetric studies on the XHA600D accelerator have yet been found. And unlike these references, this study speci cally analyzed the e ects of these four incident electron parameters on PDDs and OARs in di erent beam elds and the details of the benchmarking process to obtain accurate incident electron information of the XHA600D accelerator.…”

DeepBeam – A Machine Learning Framework For Tuning The Primary Electron Beam of The PRIMO Monte Carlo Software

“…proposing various experimental setups and methods of such analysis [6][7][8][9][11][12][13][14][15][16][17][18]. In the study of Almberg et al [9] an algorithm is proposed to determine values of two parameters (nominal energy and spot size) of the primary electron beam model, basing on depth and lateral photon beam profiles measured for three fields: 2x2, 10x10, and 20x20 cm2.…”

“…The last two steps require an extensive MC simulation effort while being based on a trial-and-error approach. Other studies of [13][14][15][16][17][18] are also based on a trial-and-error approach which, while being computationally demanding, offers no systematic procedure for estimating parameter values in the applied model of the primary electron beam.…”