A virtual photon energy fluence model for Monte Carlo dose calculation

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Dosimetry

Background:

• Accurate dose calculation is crucial for radiotherapy.
• Modeling medical linear accelerator (LINAC) photon beams requires precise characterization of the source.
• Existing models may be computationally intensive, especially for intensity-modulated radiation therapy (IMRT).

Purpose of the Study:

• To develop and validate a patient-independent virtual energy fluence (VEF) model for LINAC heads.
• To enable accurate and efficient dose calculation for various beam configurations.
• To provide a clinically feasible method for LINAC model commissioning.

Main Methods:

• The VEF model uses two Gaussian photon sources and one electron source with adjustable parameters.
• Analytical calculations of energy fluence distributions are performed and fitted to measured dose distributions in air.
• Depth dose curves in water are used to derive the energy spectrum, accounting for off-axis softening.
• The VEF model is integrated into the XVMC dose calculation engine and validated against experimental measurements.

Main Results:

• The VEF model accurately simulates open photon beams from different LINAC vendors.
• The model successfully predicts dose distributions and output factors in water.
• The commissioning process, using standard air and water measurements, is shown to be clinically feasible.

Conclusions:

• The VEF model provides an accurate and efficient method for simulating LINAC photon beams.
• This model is suitable for clinical applications, including IMRT, due to its computational efficiency.
• The VEF model simplifies LINAC commissioning and enhances treatment planning accuracy.