Speaker
Description
Biological effects of ionizing radiation arise from a sequence of stochastic processes, including particle interactions, radical chemistry, DNA damage induction, cellular repair, and tissue-level responses. Monte Carlo track structure simulations capture many of these early physical and chemical stages and enable mechanistic investigation of radiation quality effects. Despite this inherent stochasticity, most simulations report only mean DNA damage yields, such as average double strand breaks per cell or per unit dose, overlooking substantial variability.
In this work, PARTRAC simulations were performed for a spherical cell nucleus irradiated by ions from H to Fe across a wide range of radiation quality. Instead of focusing solely on mean values, we analyzed distributions of track length, energy deposition per track and per micrometer, and double strand breaks per track and per micrometer.
Track length followed the triangular distribution expected from random chord statistics, reflecting geometric variability. Additional stochasticity in energy deposition and the subsequent translation into DNA damage led to broad distributions of double strand breaks per track. Even for tracks of similar length and radiation type, the number of double strand breaks varied considerably, highlighting the inherent variability in DNA damage induction. These distributions propagate to the spatial organization of DNA damage foci within the nucleus, from randomly scattered to track-aligned or elongated patterns along high-LET tracks.
Our results highlight the importance of considering distributions, not just mean values, when characterizing radiation induced DNA damage. Analysis based on distributions captures the full variability of damage, supports mechanistic interpretation of experimental observations including those that deviate from the mean, and provides a more complete understanding of radiation quality and biological effects across diverse ion types.