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Question Geant vs EGS Dose-dept Disagreement 

Forum: Medical Applications
Date: 01 Dec, 2010
From: Nicole Ackerman <Nicole Ackerman>

I've been doing some simple dose simulations with GEANT, but my results disagreed when compared with a similar EGSnrc simulation. I was looking at a monoenergetic photon beam (~100 keV) going through water with a layer of another material (tungsten, for instance). For instance: 3 cm water, followed by 2 cm tungsten, then 5 cm water. The geant sim shows less initial energy deposit (I'm using the eDep scorer on a cubic mesh) than the EGS sim.

Initially I was using the Livermore physics list, and saw no difference when switching to Penelope. When I switched to EmStandardPhysics I saw my dose-depth profile become more similar to EGS in the tungsten (but the backscatter disappears). No visible difference was seen in just water. I have my cuts set to 1 nm/ 100 eV. I've attached a plot comparing the 3 physics models in Geant.

Is the problem here EGSnrc, Geant, or me? I assumed that the EmLivermore package was better for the photoelectric effect (and similar low energy studies I'm doing) and that it was sufficient on its own. Should I be using EMStandard instead/in addition? Is Geant (Livermore) getting the physics "right" and EGSnrc has it "wrong"?

I'm hoping there is a simple explanation. Thank you in advance.

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2010/12/01/17.57-15573-depthdose_physmodel.png

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1 None: Re: Geant vs EGS Dose-dept Disagreement   (michel maire - 04 Dec, 2010)
2 None: Re: Geant vs EGS Dose-dept Disagreement   (michel maire - 14 Dec, 2010)
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