Monoenergetic photon pencil beam

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The macro produces a root file with 1D histogram showing the energy deposition in  
The macro produces a root file with 1D histogram showing the energy deposition in  
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the water box along the beam line. It also produces a text file with energy and dose
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the water box along the beam line. It also produces a text file ""DoseFile.txt"" with  
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deposited at each slice of the water box. This is an example output with the default settings:
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energy and dose deposited at each slice of the water box. This is an example output  
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physics process-emstandard_opt0 and incident gamma energy of 20 MeV.  
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with the default settings: physics process emstandard_opt0 and incident gamma energy of 20 MeV.  
<pre style="color: #800000; background-color: #dcdcdc">
<pre style="color: #800000; background-color: #dcdcdc">
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  The run consists of 10000 gamma of 20 MeV through 20 cm  of Water (density: 1 g/cm3 )
  The run consists of 10000 gamma of 20 MeV through 20 cm  of Water (density: 1 g/cm3 )
</pre>
</pre>
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This is a 1D histogram showing the energy deposition in water box. The histogram comes
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from the Gamma.root files which is created after the simulation. 
[[File:/pbt/RadiotherapyWorkbook/skins/common/images/PhotonPB/Edep.png|Energy deposit per event along the beam]]
[[File:/pbt/RadiotherapyWorkbook/skins/common/images/PhotonPB/Edep.png|Energy deposit per event along the beam]]
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=== Change of physics process ===
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You can change the physics process by modifying the macro gamma.mac. The default process is
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""emstandard_opt0"" which is used in high energy experiments. Change
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<pre style="color: #800000; background-color: #dcdcdc">
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/photonPB/phys/addPhysics emstandard_opt0
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</pre>
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to
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<pre style="color: #800000; background-color: #dcdcdc">
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/photonPB/phys/addPhysics emlivermore
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</pre>
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The process ""emlivermore"" is used for low energy physics.
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Now you have to run the code again:
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<pre style="color: #800000; background-color: #dcdcdc">
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./photonPB gamma.mac
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</pre>
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=== Change the incident particle energy ===
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You can change the incident energy by modifying the macro gamma.mac. The default energy is 20 MeV.
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This energy is used in radiotherapy. You can change its value and check the efect on the energy deposit.
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Change
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<pre style="color: #800000; background-color: #dcdcdc">
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/gun/energy 20 MeV
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</pre>
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to for example
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<pre style="color: #800000; background-color: #dcdcdc">
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/gun/energy 10 MeV
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</pre>
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and run the code:
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<pre style="color: #800000; background-color: #dcdcdc">
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./photonPB gamma.mac
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</pre>
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Keep in mind that the primary particle generation is done at /PhotonPB/src/PrimaryGeneratorAction.cc
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<pre style="color: #800000; background-color: #dcdcdc">
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fParticleGun  = new G4ParticleGun(1);
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G4ParticleDefinition* particle = G4ParticleTable::GetParticleTable()->FindParticle("proton");
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fParticleGun->SetParticleDefinition(particle);
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fParticleGun->SetParticleEnergy(160*MeV); 
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fParticleGun->SetParticleMomentumDirection(G4ThreeVector(1.,0.,0.));
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...
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G4double x0 = -0.5*(fDetector->GetAbsorSizeX());
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G4double y0 = 0.*cm, z0 = 0.*cm;
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...
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fParticleGun->SetParticlePosition(G4ThreeVector(x0,y0,z0));
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</pre>
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The line
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<pre style="color: #800000; background-color: #dcdcdc">
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fParticleGun  = new G4ParticleGun(1);
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</pre>
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means that only one particle is generated and incident from coordinates x0,y0,z0. The default number of
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events is set to 10000. Therefore 10000 particles are incident to the water box.
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=== Change the material of the phantom ===
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This experiment is to compute the energy deposition of photons in a water box. However,
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there is an option to change the box material from water to lead. This can be done in the
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gamma.macro.
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Change
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<pre style="color: #800000; background-color: #dcdcdc">
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/photonPB/det/setMat Water
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</pre>
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to
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<pre style="color: #800000; background-color: #dcdcdc">
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/photonPB/det/setMat Lead
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</pre>
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and run the code
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<pre style="color: #800000; background-color: #dcdcdc">
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./photonPB gamma.mac
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</pre>

Revision as of 10:12, 16 July 2014

Retrieved from "https://www.hep.ucl.ac.uk/pbt/RadiotherapyWorkbook/index.php/Monoenergetic_photon_pencil_beam"
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