Numerical insight into the Dual Radiation Action Theory

Area of Science:

• Radiation biology
• Biophysics
• Nuclear physics

Background:

• Understanding DNA damage mechanisms is crucial for radiation protection and therapy.
• The Dual Radiation Action Theory (DRAT) describes radiation-induced cell killing based on one- and two-track events.
• Heavy charged particles like protons and alpha particles present unique radiobiological challenges due to their high linear energy transfer (LET).

Purpose of the Study:

• To numerically investigate the first and second-order mechanisms of lethal DNA lesion induction by protons and alpha particles.
• To validate the Dual Radiation Action Theory (DRAT) for heavy charged particles using a detailed atomic-resolution model of genetic material.
• To determine the dose-dependent relationship between radiation type, DNA damage, and biological effectiveness.

Main Methods:

• Utilized a high-resolution geometrical model of genetic material (5.47 × 10^9 base pairs) up to the chromatin level.
• Employed the GEANT4-DNA Monte Carlo code to simulate ion interactions with the DNA model.
• Quantified lethal lesions from one- and two-track mechanisms and estimated the alpha/beta ratio and relative biological effectiveness (RBE).

Main Results:

• The number of lethal lesions followed dose and squared dose dependencies, consistent with DRAT predictions.
• Estimated RBE values aligned with experimental results for LET below approximately 100 keV/μm.
• Observed an increase in the beta parameter with LET, leading to an increasing alpha/beta ratio, and explained the saturation of the alpha parameter at higher doses (> 6 Gy).

Conclusions:

• The study provides numerical insights into DRAT mechanisms for heavy particles, linking physical parameters to biological outcomes.
• The alpha parameter in cellular survival curves is influenced by physical alpha and beta parameters and specific energy deposition per track.
• Findings contribute to a better understanding of radiation-induced DNA damage and its biological consequences, particularly for proton and alpha particle therapy applications.