Simulation of Siemens ONCOR™ Expression linear accelerator using phase space in the MCNPX code

• The Percentage Depth Dose (PDD), the profiles, have been calculated megavoltage beams.
• The spectrum showed that the material that composes the target increases the image quality.
• The characterization of medical accelerators for dose optimization high importance for engineering.

In this work, the main components of Siemens ONCOR™ Expression linear accelerator have been modeled using the Monte Carlo code MCNPX. The model thus developed has been used in the validation of the 6 and 15 MV photon beams, applying the phase space technique. The Percentage Depth Dose (PDD), the profiles, and the photon spectrum of the 10 × 10 cm2 field have been calculated for both megavoltage beams. The higher emission probability in the low-energy portion of the photon spectrum has been determined for the 6 MV beam, in order to enhance the image of the Cone Beam Computed Tomography with megavoltage beam, using the Flat Panel portal. Results obtained for the Percentage Depth Dose have shown an agreement of better than 1% with the measured values in the regions beyond the build-up, for both beams. The profiles simulated at different depths have shown a good agreement with experimental values, below of the tolerances established. The photon spectrum calculated for the 10 × 10 cm2 field show that energies lower 250 keV tend to present a higher probability of emission, especially when the 6 MV beam is considered. This is probably due to the use of low density materials in the target of the linear accelerator.