Investigation of factors influencing the accuracy of Monte Carlo simulation of a Siemens linear accelerator

Golshan Mahmoudi, Parvaneh Shokrani, Alireza Amouheidari, Maryam Atarod


Introduction: One of the limitations of treatment planning system (TPS) algorithms is related to dose calculation in heterogeneous media and interfaces. Dose calculation with Monte Carlo (MC) simulation can significantly reduce this error. The purpose of this study was to investigate factors that influence the simulation accuracy of a Siemens ONCOR treatment head using MC method.
Methods: BEAMnrc, DOSEXYZnrc MC code (Version. 4-r2.3.1) and the general information about Siemens linacs, provided by the manufacturer, were used. Percent Depth Dose (PDD) and profiles, for 18 MV photon beams and 40×40 cm2 field size in water phantom were compared to ionization chamber measurement. Impact of factors such as beam energy, full width at half maximum (FWHM), flattening filter, primary collimator geometry, distance of scoring plane to isocenter and area of scoring plane on PDD, profiles and out of field dose on the MC simulation accuracy were investigated.
Results: The main affecting factors on MC simulation were initial electron beam energy and geometry of primary collimator for PDD and profile, respectively, and shape and density of flattening filter, primary collimator, distance of source to target and target to flattening filter for FWHM.
Conclusion: Result of this study can be used for optimizing dose calculations in heterogeneous media and interfaces and investigation of TPS calculations accuracy for Siemens ONCOR linac.

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