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     Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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                          GAMMA THERAPY

                   I.Gudovska, V.Ivanchenko, S.Larsson
            Karolinska Institute & Hospital, Stockholm, Sweden
                       CERN, Geneva, Switzerland


Electron beam of 50 MeV converted on target. All charged particles removed
from the beam after the target. Gamma beam irradiate a water phantom.
In front of the phantom a thin CheckVolume is placed to score gamma
beam properties. Inside the phantom a score volume is placed to calculate 
radial radiation dose distribution.


                           GEOMETRY


GammaTherapy application geometry consists of along z:

1. Generator of electrons directed along z-axis
2. Target1 (Be, W)
3. Target2 (W, Cu)
4. GasVolume (He)            all charged particles are killed inside 
5. CheckVolume (Air)         is sensitive for scoring in front of thephantom
6. Phantom (H2O)             is sensitive for radioactive dose calculation
7. Absorber in Phantom (H2O) is sensitive for transverse dose calculation

World volume consists of Air.


                           STEERING

Geometry and other parameters can be defined by G4 UI commands.

Following macro files are prepared for different targets used in the real
setup: be.in (thin Be target), be_w.in (thick BeW target), cu_w.in (thick
Cu W target).

Following Physics Lists can be activated via UI commands:

/testem/phys/addPhysics       standard
/testem/phys/addPhysics        g4v52
/testem/phys/addPhysics       penelope
/testem/phys/addPhysics       lowenergy

For interactive mode G4 visualization options and variables should be
defined, then the example should be recompiled:

gmake visclean
gmake

The vis.mac file can be used an example of visualization.


                          HISTOGRAMS

To use histograms any of implementations of AIDA interfaces should
be available (see http://aida.freehep.org).

A package including AIDA and extended interfaces also using Python
is PI, available from: http://cern.ch/pi .

Once installed PI or PI-Lite in a specified local area $MYPI, it is
required to add the installation path to $PATH, i.e. for example,
for release 1.2.1 of PI:

setenv PATH ${PATH}:$MYPI/1.2.1/app/releases/PI/PI_1_2_1/rh73_gcc32/bin

CERN users can use the PATH to the LCG area on AFS.

Before compilation of the example it is optimal to clean up old 
files:

gmake histclean
setenv G4ANALYSIS_USE 1
gmake

Before running the example the command should be issued:

eval `aida-config --runtime csh`

It is possible to choose the format of the output file with 
histograms using UI command:

/testem/histoName type
/testem/histoType type

The following types are available: hbook, root, xml.