Calculation of microdosimetric spectra for protons using Geant4-DNA and a μ-randomness sampling algorithm for the...

Area of Science:

• * Physics
• * Radiation Biology
• * Computational Science

Background:

• * Microdosimetry quantifies radiation quality by analyzing stochastic energy deposition in microscopic structures.
• * Understanding radiation effects at the nanoscale is crucial for radiobiology and radiation protection.
• * Nanometric structures like DNA, nucleosomes, and chromatin fibers are key targets for radiation-induced damage.

Purpose of the Study:

• * To calculate microdosimetry quantities for nanometric structures irradiated with protons using the μ-randomness method and Geant4-DNA.
• * To investigate the correlation between microdosimetry parameters and DNA damage.
• * To validate Geant4-DNA code parameters by comparing simulation results with existing data.

Main Methods:

• * Simulation of proton irradiation (0.5-100 MeV) on a 6 μm water sphere using Geant4-DNA.
• * Calculation of microdosimetric quantities (frequency- and dose-mean lineal and specific energies) in cylindrical volumes (23x23 Å to 300x300 Å).
• * Application of the μ-randomness method to define random positions and directions of convex bodies within the water sphere.
• * Comparison of calculated microdosimetric parameters with results from the KURBUC code.

Main Results:

• * Calculated ranges for frequency-mean lineal energy [2.34,47.06] keV/μm and dose-mean lineal energy [10.40,68.55] keV/μm.
• * Calculated ranges for frequency-mean specific energy [0.04,39.38]×10⁶ cGy and dose-mean specific energy [0.16,90.29]×10⁶ cGy.
• * Specific energy results showed higher sensitivity to volume changes in smaller cylinders.
• * Frequency-mean specific energy showed better agreement with KURBUC results than dose-mean specific energy.

Conclusions:

• * Geant4-DNA successfully calculated microdosimetry parameters for proton irradiation, accounting for stochastic energy deposition.
• * A clear correlation was observed between microdosimetry parameters and DNA double-strand break yields for volumes comparable to DNA.
• * The study provides a foundation for quantifying radiation effects on DNA damage using microdosimetry principles.