[Gate-users] Annulus cylinder source/phantom pair in Gate 6.2

[Marc Chamberland]

Hi Leo,

I'm replying to the mailing list because I think this might be relevant to other people.


Your macro commands looked fine, so my first thought was there must be a problem with the visualization. After a bit of snooping in the source code, I tracked down the source visualization to a call to:

void G4SPSPosDistribution::GeneratePointsInVolume()
{
  G4ThreeVector RandPos;
  G4double tempx, tempy, tempz;
  G4double x, y, z;
  x = y = z = 0.;
  if(SourcePosType != "Volume" && verbosityLevel >= 1)
    G4cout << "Error SourcePosType not Volume" << G4endl;
  //Private method to create points in a volume

[Marc's note: I'm skipping some irrelevant lines here] 

  else if(Shape == "Cylinder")
    {
      x = Radius*2.;
      y = Radius*2.;
      while(((x*x)+(y*y)) > (Radius*Radius))
	{
	  x = posRndm->GenRandX();
	  y = posRndm->GenRandY();
	  z = posRndm->GenRandZ();

	  x = (x*2.*Radius) - Radius;
	  y = (y*2.*Radius) - Radius;
	  z = (z*2.*halfz) - halfz;
	}
    }


(This is from the file G4SPSPosDistribution.cc within Geant4's source code.)

As you can see, the visualization of a cylindrical (or annulus) volume does NOT take into account the inner radius (radius0); it only takes into account the outer radius! This is why the source looks wrong. I would consider this a bug in Geant4.

It should not be too hard to fix by yourself, though.

Cheers,
Marc



__________________________

Marc Chamberland, MSc
PhD candidate
Department of Physics
Carleton University
Ottawa (ON)

On 2013-06-28, at 9:23 AM, Leo Read <leoread at gmail.com>
 wrote:

> Hi Marc,
> 
> Thank you for your prompt reply. The reason I posted is because I tried to write the code (see below the figure) to define my annular phantom but got the following result. I must be missing something very trivial as I can't seem to figure out how to get the source (white dots) to stay occupy the same volume as the phantom.
> 
> 
> 
> I'd greatly appreciate any advice. I will post the final solution to the forum once I have it sorted out.
> 
> Thanks,
> Leo
> 
> ##code to define annular phantom
> /gate/world/daughters/name myphantom
> /gate/world/daughters/insert cylinder
> /gate/myphantom/setMaterial Water
> /gate/myphantom/geometry/setRmax   32 cm
> /gate/myphantom/geometry/setRmin   30 cm
> /gate/myphantom/geometry/setHeight 15 cm
> 
> /gate/myphantom/vis/forceSolid
> /gate/myphantom/vis/setColor magenta
> /gate/myphantom/vis/setVisible 1
> 
> /gate/myphantom/attachPhantomSD
> 
> ##code to define source to occupy region defined by the phantom
> /gate/source/addSource             mysource
> /gate/source/mysource/setActivity     100000. becquerel
> /gate/source/mysource/gps/particle    gamma
> /gate/source/mysource/setType         backtoback
> /gate/source/mysource/gps/energytype     Mono
> /gate/source/mysource/gps/monoenergy    511 keV
> 
> /gate/source/mysource/gps/angtype    iso
> #/gate/source/mysource/gps/mintheta     90 deg
> #/gate/source/mysource/gps/maxtheta     90 deg
> #/gate/source/mysource/gps/minphi     0 deg
> #/gate/source/mysource/gps/maxphi     360 deg
> 
> /gate/source/mysource/gps/type         Volume
> /gate/source/mysource/gps/shape     Cylinder
> /gate/source/mysource/gps/radius0     30 cm
> /gate/source/mysource/gps/radius     32 cm
> 
> /gate/source/mysource/gps/halfz     7.5 cm
> 
> /gate/source/mysource/gps/centre         0.0 0.0 0. mm
> 
> /gate/source/list
> 
> /gate/source/mysource/visualize         2000 white
> 
> 
> 
> On Fri, Jun 28, 2013 at 8:07 AM, Marc Chamberland <MarcChamberland at cmail.carleton.ca> wrote:
> Hi Leo,
> 
> I'm not sure what you mean. Gate can create a cylindrical annulus: a cylinder with a different inner and outer radius. This can be used for either a phantom or a source.
> 
> For example, if you want your source to be inside the phantom, you just have to define your source to be exactly the same shape as the phantom.
> 
> Am I missing something?
> 
> Marc
> 
> 
> 
> __________________________
> 
> Marc Chamberland, MSc
> PhD candidate
> Department of Physics
> Carleton University
> Ottawa (ON)
> 
> On 2013-06-28, at 7:56 AM, Leo Read <leoread at gmail.com>
>  wrote:
> 
>> Hello all,
>> 
>> I'm new to Gate (using version 6.2) and it seems like there isn't a simple solution to model the commonly used annulus cylindrical phantom with the source embedded inside. Could somebody please help?
>> 
>> Thank you all for your time and assistance.
>> 
>> Best regards,
>> Leo
>> _______________________________________________
>> Gate-users mailing list
>> Gate-users at lists.opengatecollaboration.org
>> http://lists.opengatecollaboration.org/mailman/listinfo/gate-users
> 
> 
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