Modeling of Production Process of DNA Damage by Irradiation with Monochromatic X-rays around K-edge of Phosphorus

The mechanism of DNA strand break induction due to K-shell photoabsorption of DNA constituent phosphorus was studied by computer simulation. Photon induced Auger process in DNA solution was modeled and introduced to the Monte Carlo simulation code DBREAK, which allows the estimation of DNA strand break production on pBR322 plasmid DNA in aqueous solution. The simulation was carried out for the direct energy deposition events and the attack of water radicals generated in the water containing OH radical scavenger. Experimental results on the single(ssb) and double-strand break (dsb) yields in DNA solution could be reproduced well by our simulation modeling the photon induced Auger process. The calculated induction efficiency of ssb and dsb on DNA was enhanced by K-shell photoabsorption of phosphorus. It was found that the efficiency of strand breaks following photoabsorption of phosphorus K-shell was higher than those of other atoms and shells. The main pathway of the enhancement was concluded that the direct energy deposition in DNA and hydration shell by low-energy Auger electrons.