A Monte Carlo multiple source model applied to radiosurgery narrow photon beams

Area of Science:

• Medical Physics
• Radiotherapy Physics
• Computational Dosimetry

Background:

• Monte Carlo (MC) methods are crucial for accurate dose calculations in radiotherapy.
• Simulating narrow photon beams in radiosurgery using traditional MC methods presents efficiency challenges, impacting the quality of phase space data (PSD) and dose accuracy.
• Existing methods struggle with the computational demands of simulating narrow photon beams for radiosurgery.

Purpose of the Study:

• To develop and validate a multiple source model for enhancing the quality of simulated phase space data (PSD) in radiosurgery.
• To reduce the computational time and storage requirements associated with MC simulations of narrow photon beams.
• To improve the accuracy of dose calculations for radiosurgery treatments using MC methods.

Main Methods:

• A multiple source model was developed based on full MC simulation of a linear accelerator head and collimators using MCNP4C.
• Characterization of particles from the accelerator and collimators identified eight virtual photon sources with stored spatial, energy, and directional distributions.
• Reconstructed PSDs were generated using a sampling procedure within the DPM code, and dose distributions were calculated in a water phantom.

Main Results:

• The developed model accurately calculates dose distributions in a water phantom for various collimators.
• Depth dose curves showed errors below 2.5% (at 2 sigma) up to 202.5 mm depth.
• Profile deviations between measured and calculated values were less than 2.5% or 1 mm at various depths.

Conclusions:

• The multiple source model significantly enhances PSD quality and reduces computational demands for radiosurgery MC simulations.
• This approach enables accurate dose distribution calculations, meeting clinical requirements for radiosurgery.
• The validated model offers a more efficient and precise tool for radiation therapy planning and research.