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Validation of Monaco TPS Monte Carlo based calculation algorithm through Monte Carlo particle transport simulation

The most accurate absorbed dose calculation in radiation oncology nowadays is provided by Monte Carlo (MC) based algorithms. Such algorithms inherently calculate absorbed dose to medium in medium Dm, m. They can also provide data as absorbed dose to water in medium Dw, m by conversion based on SpencerAttix extension of Bragg-Gray small cavity theory. These two absorbed dose concepts do not necessarily provide similar results, which is particularly prominent in bone structures. Monte Carlo based algorithms used in radiation oncology use several approximations and simplifications to speed up calculation time. Furthermore, they do not use data of chemical composition of media which is the case with generalised MC particle transport simulation algorithms (e.g. MCNP, EGS, GEANT…). Therefore, an investigation of the material chemical composition impact on calculation accuracy was performed comparing calculations obtained using Monte Carlo N-Particle code® (MCNP) and a clinical MC based algorithm. Absorbed dose data acquired by MCNP was used as reference data. Investigation of absorbed dose calculation accuracy was performed for 6MV X-ray beam (Siemens Oncor Expression linear accelerator) in various geometries of different complexities. Comparison between two MCTPS dose calculation options and MCNP calculations in simple (homogeneous) and different heterogeneous geometries was performed using 13 different materials with mass densities ranging from 0.2 g/cm3 to 2.17 g/cm3 (Table 1). The MCNP calculations were performed by assigning material chemical composition and mass density (MCNPMEDIUM). The absorbed dose was calculated as Dm, m. The Dm, m calculation shows very good agreement with standard MCNP calculations except for low- density medium. Therefore, the improvement of the accuracy of MCTPS Dm, m calculation option in low- density medium may be the further step of the research. Nevertheless, the results obtained in this work indicate that Dm, m could be regarded as the preferable dose calculation option.

RT, TPS Monte Carlo based, MCNP

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