Simulation of Medical Linear Accelerators with PENELOPE - Radiation Damage in Biomolecular Systems - page 315

The first Monte Carlo simulation of a medical linac was done by M. Udale in
1988 [ 2 ]. A few years later D.W.O. Rogers and co-workers introduced the code
BEAM for simulation of medical linacs [ 3 ]. After these pioneering works, the
field has observed an exponential growth in the number of publications related to
Monte Carlo simulation of linacs. Such growth has derived in efforts to implement
Monte Carlo simulations in the clinical routine within radiotherapy units [ 4 , 5 ].
The first simulation of a linac with PENELOPE appeared in 2001 [ 6 ]. After that
work, the PENELOPE code system has been increasingly used for linac simulation
(e.g., [ 7 - 11 ]).

19.2 The PENELOPE code system

PENELOPE is a set of FORTRAN subroutines written for performing general-
purpose Monte Carlo simulations of radiation transport in arbitrary materials and
complex geometries [ 12 , 13 ] 1 . The code can simulate the coupled transport of
electrons, photons and positrons in the energy range from 50 eV up to 1 GeV.
PENELOPE includes a material database with the first 99 elements of the periodic
table as well as 181 compounds. Should a compound not present in the database be
required, this can be created by means of its stoichiometric formula.
Geometries in PENELOPE can be programed with the code PENGEOM included
in the distribution. With PENGEOM it is possible to define geometries by grouping
quadric surfaces to form bodies. Bodies, in its turn, can also be grouped to form
more complex structures. When dealing with elaborate geometries, such as a linac,
the way bodies are defined and grouped is critical in terms of simulation speed.
PENELOPE is a subroutine package, therefore, end users are responsible for
writing a steering main program. Examples of main programs are provided with
the distribution package. Although this approach is general enough for dealing
with a wide range of applications, it imposes a burden on users that only need to
simulate some specific linacs. These users are required to write their own geometry
file and to code or adapt a main program. These tasks are error-prone and require
some knowledge of physics, Fortran programing and PENGEOM syntax. In order to
ease these tasks several codes have been published. The following codes are not
part of the PENELOPE distribution, however they are useful for users interested in
simulating linacs.

1 Distributed at the OECD Nuclear Energy Agency Data Bank ( http://www.nea.fr )andthe
Radiation Safety Information Computational Center ( http://www-rsicc.ornl.gov ).