Modeling the head of PRIMUS linear accelerator for electron-mode at 10 MeV for different applicators

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Dosimetry

Background:

• Accurate modeling of linear accelerator (LINAC) heads is crucial for precise radiation therapy dose calculations.
• Monte Carlo (MC) simulations offer a powerful tool for simulating complex radiation transport phenomena.
• Validation of simulation models against experimental data ensures their reliability in clinical settings.

Purpose of the Study:

• To validate the use of MC simulation for modeling the Primus LINAC head.
• To estimate key dosimetric parameters including energy fluence distribution (EFD), percentage depth dose (PDD), and beam profiles.
• To assess the accuracy of the simulation for various applicator sizes.

Main Methods:

• The BEAM_NRC code, based on EGS_NRC, was employed to model the 10 MeV electron beam of the Primus LINAC.
• Simulations were performed for multiple applicator sizes (10x10, 15x15, 20x20 cm²).
• Phase space data from BEAM_NRC were used as input for DOSXYZ_NRC and BEAMDP to calculate EFD, PDD, and beam profiles.

Main Results:

• Excellent agreement was observed between MC simulation results and measured PDD and off-axis dose profiles in a water phantom.
• Key PDD parameters (R₁₀₀, R₉₀, R₈₀, R₅₀) showed discrepancies <2 mm, with a minor deviation of 6 mm in R₁₀₀ for the 15x15 cm² applicator.
• Surface dose discrepancies were <3%, rapidly decreasing to 0% within 2.4 mm, and beam profile differences ranged from 2% to 3%.

Conclusions:

• The MC simulation using the BEAM_NRC code accurately models the Primus LINAC head.
• The validated MC model provides reliable estimations of EFD, PDD, and beam profiles.
• This approach enhances the accuracy of dose calculations in radiation therapy planning.