Experimental characterisation of a proton kernel model for pencil beam scanning techniques

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Science

Background:

• Proton therapy utilizes scanned proton beams for precise dose delivery.
• Accurate simulation of proton beam characteristics, including the low-dose envelope, is critical for treatment planning.
• Variations in nozzle geometry and beam source modeling can impact simulation accuracy.

Purpose of the Study:

• To perform Monte Carlo simulations of a proton pencil beam scanning machine.
• To characterize the low-dose envelope of scanned proton beams.
• To assess the impact of nozzle geometry approximations on dose distribution accuracy.

Main Methods:

• Utilized Geant4 Monte Carlo platform (TOPAS) for simulations.
• Conducted experimental measurements in water using a 2D ion chamber array detector.
• Investigated various beam source parameterizations, including a Double Gaussian model.
• Analyzed proton phase spaces at the nozzle exit.

Main Results:

• Achieved excellent agreement between simulations and experimental dose distributions for proton energies > 160 MeV.
• Observed minor discrepancies at lower energies (100-160 MeV), indicating sensitivity to treatment head modeling.
• Identified the first ionization chamber as a significant factor in low-energy beam tail components.
• Proposed parameterizations successfully reproduced the low-dose envelope and matched measured data.

Conclusions:

• Monte Carlo simulations, particularly with refined source parameterizations, can accurately model proton beam dose distributions.
• Accurate modeling of the treatment nozzle and its components is essential for precise low-energy proton beam simulations.
• The findings support the use of advanced simulation techniques for optimizing proton therapy treatment planning.