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Forum: Geometry
Re: None Performance of homogeneous voxelised phantom (Sven Lotze)
Date: 08 Nov, 2007
From: Makoto Asai <Makoto Asai>

 > After some reading, I realise that my implementation is probably
> worst case as performance is concerned, ...

I'm afraid so. But not due to the scorer but most-likely
due to the way how you implemented your voxels. Could 
you please post the code where you implement the voxel 
geometry? In particular, how did you divide the phantom?

Makoto


> -----Original Message-----
> From: Sven Lotze [mailto:lotze@physik.rwth-aachen.de] 
> Sent: Thursday, November 08, 2007 3:23 AM
> To: publichypernews
> Subject: Performance of homogeneous voxelised phantom
> 
> *** Discussion title: Geometry
> Email replies to PublicHyperNews@slac.stanford.edu must include:
>   In-Reply-To: <"/geometry/814"@geant4-hn.slac.stanford.edu>
>   Subject: ...change this to be about your reply.
> 
> Hi,
> 
> in my simulation I have a homogeneous water phantom voxelised in 
> 3d by dividing the box geometry into many G4Boxes in the tracking
> geometry and attaching a primitive scorer for deposited energy
> to each. As I increase the resolution (smaller voxels), calculation 
> time skyrockets.
> 
> After some reading, I realise that my implementation is probably
> worst case as performance is concerned, because the tracking has
> to stop at every voxel boundary. The alternatives I see now are
> 
> A) using a parallel readout geometry and do the scoring there, 
>    like e.g. in the hadrontherapy example
> 
> B) doing it manually by using G4UserStepping action, like
>    in TestEM11/12.
> 
> I would assume that B should be faster, as more low level
> G4 functions are used - is that correct?
> 
> On the other hand, as I have to limit the step length as
> done in TestEM11/12 according to voxel size, doesn´t that
> lead to the same problems as my original geometry with 
> small volumes limiting the steps?
> 
> Looking at TestEM11/12, for the deposited energy in each 
> step a position along the step is randomly chosen before
> filling it to a histogram. Why is that necessary if max.
> step size is limited corresponding to voxel (=bin) size 
> anyway? Why not deposit it at the center of the step?
> 
> Thanks for your help!
> 
> Sven
> 
> 

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