Radiation Protection Dosimetry Advance Access originally published online on May 19, 2007
Radiation Protection Dosimetry 2007 126(1-4):457-462; doi:10.1093/rpd/ncm092
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Monte-Carlo study of energy deposition by heavy charged particles in sub-cellular volumes
1 Medical Physics Laboratory, University of Ioannina Medical School, Ioannina 45110, Greece
2 Department of Mechanical Engineering, National Technical University of Athens, Athens 157 10, Greece
3 School of Physics, University of Hyderabad, Hyderabad 500 046, India
4 Nuclear Medicine Department, University Hospital of Ioannina, Ioannina 451 10, Greece
5 USRA, NASA Johnson Space Center, Houston, Texas 77058, USA
* Corresponding author: hooshang.nikjoo1{at}jsc.nasa.gov
Detailed-history Monte-Carlo code is used to study the energy deposition from proton and alpha particle tracks at the sub-cellular level. Inelastic cross sections for both the vapour and liquid phases of water have been implemented into the code in order to explore the influence of non-linear density effects associated with the condensed-phase cellular environment. Results of energy deposition and its straggling for 0.5 to 5 MeV amu–1 protons and alpha particles traversing or passing near spherical volumes of 2–200 nm in diameter relevant to DNA- and chromosome-size targets are presented. It is shown that the explicit account of 
-ray transport reduces the dose by as much as 10–60%, whereas stochastic fluctuations lead to a relative uncertainty ranging from 20% to more than 100%. Protons and alpha particles of the same velocity exhibit a similar -ray effect, whereas the relative uncertainty of the alphas is almost half that of protons. The effect of the phase is noticeable (10–15%) mainly through differences on the transport of -rays, which in liquid water have higher penetration distances. It is expected that the implementation of such results into multi-scale biophysical models of radiation effects will lead to a more realistic predictions on the efficacy of new radiotherapeutic modalities that employ either external proton beam irradiation or internal alpha-emitting radionuclides.