Deterministic photon transport calculations in general geometry for external beam radiation therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Physics

Background:

• Accurate dose calculation is crucial for effective radiation therapy planning.
• Monte Carlo (MC) methods are widely used but can be computationally intensive.
• Deterministic methods offer a potential alternative for photon transport calculations.

Purpose of the Study:

• To present a deterministic method for 3D photon transport calculations in LINAC heads and patient geometries.
• To obtain accurate dose distributions for radiation therapy planning.
• To compare the deterministic method's results with Monte Carlo simulations.

Main Methods:

• Solving the Boltzmann equation in 3D using the method of characteristics for photon flux density.
• Employing ray tracing routines similar to those in MC codes.
• Developing a special treatment for scattering from LINAC head components.
• Calculating water kerma distribution from uncollided and collided photon flux.

Main Results:

• The deterministic method provides space, energy, and direction-dependent photon flux density.
• Water kerma distributions were computed for various source spectra and field sizes.
• Results showed agreement with Monte Carlo values within MC uncertainties for kerma in the beam.
• The method accurately represents scattering from accelerator head components.

Conclusions:

• The deterministic method is a rigorous, first-principles approach for 3D photon transport.
• It can serve as a superior alternative to Monte Carlo calculations for specific problems in therapy planning.
• Further development is required to incorporate 3D electron transport capabilities.