A beam model for focused proton pencil beams.

Area of Science:

• Medical physics
• Computational dosimetry
• Radiation oncology

Background:

• A beam model was developed for Monte Carlo simulations of the IBA pencil beam scanning dedicated nozzle at Skandion Clinic.
• The model accounts for beam convergence downstream of the nozzle exit due to vacuum traversal.

Purpose of the Study:

• To develop and validate a beam model for accurate Monte Carlo simulations of the IBA pencil beam scanning nozzle.
• To assess the model's suitability for quality assurance and patient motion studies.

Main Methods:

• Modeled beam phase space distributions (angular, spatial, energy) at nozzle exit using single Gaussians with seven energy-dependent parameters.
• Determined model parameters from measured beam profiles and depth dose distributions.
• Verified the model by comparing measured and GATE-simulated relative dose distributions using machine log files.

Main Results:

• GATE simulations using the developed beam model accurately reproduced measured data.
• Gamma index analysis showed >95% global pass rates (3%/2 mm) for all depths, confirming high accuracy.

Conclusions:

• The developed beam model is sufficiently accurate for use with GATE simulations.
• The model is suitable for applications like quality assurance and patient motion studies with IBA pencil beam scanning nozzles.