Analytical scatter kernels for portal imaging at 6 MV

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Science

Background:

• Accurate modeling of X-ray photon scatter is crucial for quantitative electronic portal imaging (EPI) in radiation therapy.
• Existing analytical models face limitations with larger field sizes and varying scatterer-to-detector air gaps.
• Monte Carlo simulations provide detailed scatter information but are computationally intensive.

Purpose of the Study:

• To investigate and develop accurate analytical and semi-analytical models for X-ray photon scatter kernels at 6 MV.
• To evaluate model performance against Monte Carlo simulations for clinical relevance.
• To improve scatter modeling for enhanced accuracy in electronic portal imaging.

Main Methods:

• Developed a fully analytical model treating single Compton scatter exactly and higher orders approximately.
• Utilized Monte Carlo simulations to determine the effective location of multiple scatter sources.
• Investigated a semi-analytical model fitting an analytical function to Monte Carlo data for higher-order scatter.

Main Results:

• The initial analytical model achieved 1% accuracy for field sizes up to 100 cm2 and air gaps >30 cm.
• Monte Carlo results indicated the multiple-scatter source is near the scatterer's exit surface.
• The refined semi-analytical model demonstrated 1% accuracy for field sizes up to 900 cm2 and phantom thicknesses up to 50 cm, with air gaps down to 20 cm.

Conclusions:

• The fully analytical model is limited for larger field sizes due to scatter source assumptions.
• The semi-analytical model, incorporating Monte Carlo-derived scatter source characteristics, significantly enhances accuracy and clinical applicability.
• This improved scatter modeling is vital for precise dose calculations and image analysis in radiation therapy using EPI.