Technical note: A PBS source model based independent dose calculation frame on TOPAS MC

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Science

Background:

• Monte Carlo (MC) simulations are crucial for accurate dose calculation in particle therapy.
• Existing MC platforms often rely on specific treatment planning systems (TPS), limiting their versatility.
• Developing an independent MC platform enhances flexibility and applicability in research and clinical settings.

Purpose of the Study:

• To establish a versatile Monte Carlo (MC) dose calculation platform independent of treatment planning systems (TPS).
• To create a comprehensive methodology for building such a platform for proton therapy.
• To enable accurate dose verification and support scientific research in particle therapy.

Main Methods:

• Optimized phase space parameters and beam source models in the source emission plane.
• Developed an automated method to convert patient plans into executable MC scripts for TOPAS MC software.
• Established a library of source model parameters for reproducible simulations.

Main Results:

• Achieved excellent agreement between simulated and measured beam spot sizes (<0.3 mm).
• Demonstrated high accuracy in depth-dose curve falloff (<0.1 mm) and point-to-point dose differences (<0.7%).
• Attained 100% 3D gamma passing rates for spread-out Bragg peaks and high rates for patient plans (99.96%-100%).

Conclusions:

• Successfully developed a comprehensive MC framework for pencil beam scanning (PBS) proton therapy.
• The framework utilizes a well-defined beam source model for accurate dose calculations.
• This methodology facilitates the development of dose verification tools and advances scientific research in particle therapy.