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Microscopic Monte Carlo Simulation for DNA Damage Calculations with Oxygen Distribution

Y Lai1, X Jia2, Y Chi1*, (1) University of Texas at Arlington, Arlington, TX, (2) The University of Texas Southwestern Medical Ctr, Dallas, TX

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Oxygen is known to play an important role in DNA damages induced by radiation. However, to reduce computational costs, oxygen is often ignored or treated as a constant continuum background that can scavenge radiolysis in the chemical stage of Monte Carlo simulation. This work reports our recent progress on a new open-source high-performance GPU-based MC package--gMicroMC, with an add-on module to consider the chemical reactions with oxygen in a step-by-step fashion.

Methods: gMicroMC simulated the physical, physicochemical and chemical stages of water radiolysis and computed the induced DNA damage with a realistic lymphocyte cellular nucleus model in G0/G1 phase. Oxygen molecules are assumed to dissolve uniformly inside the cellular nucleus, whose number is calculated from given concentration. We then expanded the initial ten mutual reactions into twenty-one reactions for considering oxygen. The oxygen effect was demonstrated by computing the yield evolution of all species under different oxygen concentrations for one 4.5 keV electron inside the cell nucleus. The results were averaged over 1000 runs. The corresponding effects on indirect DNA strand breaks were computed.

Results: With the chemical stage ending at 1 µs, the yield of hydrated electron and hydrogen atom were eliminated, which leads to the massive production of toxic superoxide and hydroperoxyl radicals, while that of hydroxyl and hydroperoxide only increased slightly (~5%) when oxygen concentration changed from 0% to 21%. Our simulation also indicated that it required ~10 ns to obtain an observable effect on species changes for 21% oxygen concentration. The corresponding indirect DNA damage from hydroxyl increased by 13%. The simulation time are 38 seconds and 57 seconds for oxygen concentration 3% and 21%, respectively.

Conclusion: gMicroMC can efficiently simulate the chemical stage with the presence of DMO in a step-by-step way.

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