Using a photon phase-space source for convolution/superposition dose calculations in radiation therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Dosimetry

Background:

• Accurate modeling of photon beam characteristics from linear accelerators (linacs) is crucial for precise radiation therapy.
• Traditional beam commissioning involves numerous adjustable parameters, hindering the development of unique and self-consistent dosimetric models.
• Disentangling factors like electron scatter, focal spot size, and head scatter complicates accurate dose prediction.

Purpose of the Study:

• To develop a simplified and more self-consistent method for modeling linac photon beam dosimetry.
• To reduce the number of adjustable variables in beam modeling for improved accuracy and efficiency.
• To validate a novel phase-space plane source approach for dose calculation.

Main Methods:

• Replaced traditional focal and extra-focal sources with a single phase-space plane from an EGS/BEAM simulation.
• Utilized a stochastic convolution/superposition dose engine, propagating photons through collimators and into a phantom.
• Incorporated electron contamination from the phase-space file and applied minor corrections for monitor backscatter and collimator scatter.

Main Results:

• The single phase-space photon source approach yielded accurate and self-consistent results for relative and absolute dose calculations.
• This method effectively simplified beam modeling by reducing adjustable parameters.
• Deviations were minimal (<0.5%) even for large field sizes, with corrections for specific scatter effects.

Conclusions:

• A single phase-space plane is a viable and efficient source for accurate linac photon beam modeling.
• This simplified approach enhances the self-consistency of beam models used in radiation therapy planning.
• The method offers a robust alternative for commissioning and quality assurance of medical linear accelerators.