Applications of the microdosimetric function implemented in the macroscopic particle transport simulation code PHITS.

Area of Science:

• Medical Physics
• Radiation Biology
• Computational Science

Background:

• Lineal energy is a superior index for relative biological effectiveness (RBE) compared to linear energy transfer (LET) for high-energy particles.
• Calculating lineal energy probability densities (PD) requires integrating microdosimetric track-structure simulations with macroscopic particle transport codes.

Purpose of the Study:

• To integrate a mathematical model for microdosimetric quantity PD calculation into the PHITS code.
• To enable efficient and accurate calculation of PD in macroscopic matter, accounting for stochastic effects.

Main Methods:

• Incorporated a track-structure simulation-based mathematical model into the Particle and Heavy Ion Transport code System (PHITS).
• Developed an improved PHITS version capable of calculating microdosimetric PD within reasonable computation times.

Main Results:

• The enhanced PHITS code successfully calculates microdosimetric probability densities in macroscopic matter.
• The integration allows for consideration of the stochastic nature of particle interactions.

Conclusions:

• The improved PHITS microdosimetric function is applicable to biological dose estimation in charged-particle therapy and radiation risk assessment for astronauts.
• This advancement has the potential to enhance radiological protection systems for space missions and treatment planning in particle therapy.