Rapid MCNP Simulation of DNA Double Strand Break (DSB) Relative Biological Effectiveness (RBE) for Photons, Neutrons, and Light Ions
R.D. Stewart, S.W. Streitmatter, D.C. Argento, C. Kirkby, J.T. Goorley, G. Moffitt, T. Jevremovic, and G.A. Sandison
Phys. Med. Biol. 60 8249-8274 (2015).  Download pdf 

To account for particle interactions in the extracellular (physical) environment, information from the cell-level Monte Carlo Damage Simulation (MCDS) for DNA double strand break (DSB) induction has been integrated into the general purpose Monte Carlo N-Particle (MCNP) radiation transport code system. The effort to integrate these models is motivated by the need for a computationally efficient model to accurately predict particle relative biological effectiveness (RBE) in cell cultures and in vivo. To illustrate the approach and highlight the impact of the larger scale physical environment (e.g., establishing charged particle equilibrium), we examined the RBE for DSB induction (RBE_DSB) of x-rays, ¹³⁷Cs g-rays, neutrons and light ions relative to g-rays from ⁶⁰Co in monolayer cell cultures at various depths in water. Under normoxic conditions, we found that ¹³⁷Cs g-rays are about 1.7% more effective at creating DSB than g-rays from ⁶⁰Co (RBE_DSB = 1.017) whereas 60-250 kV x-rays are 1.1 to 1.25 times more efficient at creating DSB than ⁶⁰Co.  Under anoxic conditions, kV x-rays may have an RBE_DSB up to 1.51 times as large as ⁶⁰Co g-rays.  Fission neutrons passing through monolayer cell cultures have an RBE_DSB that ranges from 2.6 to 3.0 in normoxic cells, but may be as large as 9.93 for anoxic cells.  For proton pencil beams, Monte Carlo simulations suggest an RBE_DSB of about 1.2 at the tip of the Bragg peak and up to 1.6 a few mm beyond the Bragg peak.  Bragg peak RBE_DSB increases with decreasing oxygen concentration, which may create opportunities to apply proton dose painting to help address tumor hypoxia.  Modeling of the particle RBE for DSB induction across multiple physical and biological scales has the potential to aid in the interpretation of laboratory experiments and provide useful information to advance the safety and effectiveness of hadron therapy in the treatment of cancer.

Keywords: MCDS, LET, DSB, Clustered DNA Lesions, multiscale modeling, MCNP, electron, photon, light ion, neutron, BNCT

Last updated: October 17, 2016