Development of a LINAC head model for the CyberKnife VSI-System using EGSnrc Monte Carlo system

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Modeling

Background:

• Understanding photon and electron interactions within the CyberKnife VSI-System requires accurate modeling of the LINAC head.
• Monte Carlo simulations offer a robust method for simulating these complex physical processes.

Purpose of the Study:

• To develop and validate a Monte Carlo simulation model of the CyberKnife VSI-System's LINAC head.
• To assess the accuracy of the simulation by comparing it with measured beam data.

Main Methods:

• Utilized the EGSnrc toolkit, including BEAMnrc and DOSXZYnrc user codes, for Monte Carlo simulations.
• Modeled both the circular collimators and the IRIS-aperture of the CyberKnife VSI-System.
• Determined average energy, source width, dose profiles, and output factors in a water phantom, comparing simulated and measured data.

Main Results:

• The simulation accurately predicted the average kinetic energy (6.9 MeV) and source width (0.25 cm x, 0.23 cm y).
• Simulated dose profiles achieved a global gamma criterion of 1%/1 mm against measured data for both collimation systems.
• Output factor deviations were less than 1% for field sizes >= 12.5 mm (circular collimators) and >= 10 mm (IRIS-aperture).

Conclusions:

• Monte Carlo simulations provide an exact representation of the CyberKnife VSI LINAC head's beam characteristics.
• This validated model can serve as a foundation for future patient-specific quality assurance and the study of scattering processes.