Biomedical Engineering Reference
In-Depth Information
16.6
Monte Carlo simulation of charged particle transport
in biological medium
Modeling of DNA damages from ionizing radiation is today an active and intense
field of research. As stated above, Monte Carlo methods have been widely adopted
in the radiobiology community since they can reproduce the stochastic nature of
interactions between elementary particles and matter. In this context, we aim to
develop a Monte Carlo code able to provide a full description of proton tracks
in water and DNA components over a wide impact energy range (from several
hundreds of MeV down to the Bragg peak region) including all the secondary
particle histories.
In brief - and as commonly performed in the major part of the existing step-by-
step Monte Carlo codes - the transport simulation will comprise series of random
samplings which determine
i)
the distance to the next interaction (related to the mean
free path, this latter being calculated from the total cross section),
ii)
the type of
interaction which occurs at the point selected in
i)
and
iii)
the energy and direction of
the resultant particles according to the type of interaction selected in
ii)
. These latter
will be successively determined via random samplings among the pre-tabulated
singly and doubly differential cross sections, respectively. Particular ionization or
excitation potential will be assumed as locally deposited and the incident energy
is reduced from the corresponding energy (including as well as potential and
secondary kinetic energy transfers). All these steps will be consecutively followed
for all resultant particles until their kinetic energy falls below the predetermined cut-
off value (here 10 keV for incident protons and 7.4 eV for secondary electrons what
corresponds to the water excitation threshold). Note that sub-threshold electrons will
be assumed to deposit their energy where they are created. In these conditions, the
code will provide by way of row data the coordinates of all the interaction events as
well as the type of collision together with the energy loss, the energy deposited at
each interaction point and the kinetic energy of the resultant particle(s) in the case
of inelastic collision.
In this context, all the above-reported quantum-mechanical cross sections will
be used as input data for describing the ion-induced interactions (ionization and
capture) at the multi-differential scale. Furthermore, a detailed analysis of the
influence of the target description as well as that of the quantum-mechanical model
used for describing the ionizing processes will be done.
16.7
Conclusion
Single ionization and capture of water and DNA bases impacted by heavy charged
particles of medical interest (protons and carbon ions) have been here theoretically
studied by employing two different quantum mechanical models based on the CDW-
EIS and CB1 approaches.
