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## Detailed tips

Keywords: voxel number, human model
Forum: Medical Applications
Re: how many voxels can geant4 includes? (John)
Re: Re: how many voxels can geant4 includes? (Joseph Perl)
Re: Re: how many voxels can geant4 includes? (John)
Re: Re: how many voxels can geant4 includes? (Makoto Asai)
Date: 13 Oct, 2004
From: Makoto Asai <Makoto Asai>

 ```As requested from a user for the details of the "tricks", following is my reply sent to him. > For this aim i use a voxel based phantom read by > Geant4. The total numer of voxel is 292300. Unfortunately the > maximum number that geant4 is able to handle in a simulation > is (on my machine) only 140304. Can you tell me some trick to > make G4 able to use all the 292300 voxels? I don't know why your machine cannot handle more than about 140k copies, but it is not an issue. Anyway, having a map of more than 100k entries is something that is not recommended... The tricks you can utilize are suspending tracks and use of stacking mechanism. The basic concept is - Concentrate to a small region with a smaller map. - Finalize calculation of this small region before working for another regions. Here is the recipe. 1) Divide your mother volume (which should have 292300 cubes in total) into, say, 25 boxes. All of these 25 boxes can share the same logical volume. 2) Fill 11692 (= 292300 / 25) cubes with parameterization into the box logical volume. 3) Prepare 25 waiting stacks. The number of waiting stacks can be set by SetNumberOfAdditionalStacks() method of G4StackManager. 4) Load the material map of 11692 entries which should correspond to the box where the primary particle gets into. 5) In your stepping action, once a track comes to a boundary of a box to go into the next box, suspend it. In your stacking action, push the suspended track into a waiting stack which represents the neighboring box that the track is getting into. Of course, secondary particles generated by the ordinary physics processes should be pushed into the urgent stack. 6) Continue the simulation until the urgent stack becomes empty. Once it becomes empty, choose one waiting stack which has the largest number of entries, and transfer all suspended tracks in that stack to the urgent stack. At the same moment, load another material map of 11692 entries for this new box. 7) Repeat the procedures 5) and 6) until all stacks become empty. That's it. The number 25 is just an example. You may want to tune this number to get the best performance. ```

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