MC NP 48 محاسبه بيناب و بازده توليد پرتوهاي ايكس تابش ترمزي در شتابنده هاي پزشكي با استفاده از كدمونت كارلوي

A Method for Calculation of X-rays Bremsstruhlung Spectrum and Yield Produced in Medical Accelerators using the MCNP4B Monte Carlo Code

The output X-ray spectrum characteristics is one of the required data used in radiotherapy planning dosimeter system of medical linear accelerators (linac). The purpose of this research was to propose a method for calculating the bremsstuhlung spectrum and the x-ray yield off the target of the medical accelerators. For this purpose, three different materials of Br, Al, and Pb, as the linac target materials, were exposed to a 15 MeV electron beam and their output bremsstuhlung spectrum at three different angles of 10, 30, and 60 degrees from the central axis of incident electron beam were calculated using the MCNP4B Monte Carlo code. The Thickness of the targets was assumed equal to 110% of the range of the incident electrons. The calculated Bremsstuhlung spectra were in a very good agreement with the relevant measured spectra for all the studied target materials at all the investigated angles, except for the Pb at an energy range below 300 keV for which a significant disagreement was observed. At the second part of this research for every target material the total output production and the output x-ray yields were estimated at the base of a pyramid resulted from a 120 degree solid head angle using the Monte Carlo simulation method with the MCNP4B code. Using a suitable number of track histories the Monte Carlo statistical calculation error for the calculation of the output production yield was reduced to 1%.