Fluence calculation methods in Monte Carlo dosimetry simulations

Area of Science:

• * Medical Physics
• * Computational Physics
• * Radiation Dosimetry

Background:

• * Monte Carlo (MC) methods are crucial for simulating charged-particle transport.
• * Calculating charged-particle fluence spectra is complex and information is fragmented.
• * Existing methods have limitations in accuracy and applicability.

Purpose of the Study:

• * To consolidate and compare methods for computing charged-particle fluence spectra in MC simulations.
• * To introduce and evaluate an alternative computational approach.
• * To assess the impact of positron fluence and restricted radiative energy losses on dosimetry.

Main Methods:

• * Review and theoretical analysis of common MC fluence spectrum calculation methods.
• * Development and implementation of an alternative method.
• * Ad-hoc MC simulations for comparative analysis.
• * Investigation of restricted vs. unrestricted stopping powers.

Main Results:

• * Methods apportioning track segments to energy bins are independent of segment length and energy loss, offering higher accuracy.
• * Positron fluence can contribute several percent to total restricted collisional mass energy absorption (cema), impacting accuracy if omitted.
• * Restricted radiative energy losses have a negligible influence on fluence distribution and cema calculations.

Conclusions:

• * Segment-based energy binning methods are superior for accurate fluence spectra computation.
• * Positron fluence must be considered for precise cema calculations.
• * Restricted radiative energy losses can be disregarded in most common dosimetry scenarios.