[Gate-users] Voxelized geometry and input for dosimetry simulation

[Brosch, Julia]

Dear Gate Community,

I have only just started to use Gate Monte Carlo simulations with Gate Version 8.2 in the provided virtual machine. I would like to use it for simulation of 3D dose distributions of radionuclide therapy patient data.

I started with a simplified phantom (patients CT as input for voxelized geometry + segmented kidney, filled with activity as voxelized source input; both in interfile format) and tried to follow the provided examples regarding voxelized input and the doseactor. Unfortunately, I must have done some mistakes in defining the voxelized source as it is not taken into account during simulation or maybe some commands are missing there. I attach a macro containing all the commands I've used.
Here are my questions:

  *   When I'm using the command set primaries as input, then it seems to simulate a point source (see below) instead of my activity distribution in the voxelized source. And if I'm not using it, it is not simulating any events.

[cid:image002.jpg at 01D4F609.B4EA75B0]

Could you please help me to find my mistake why GATE is not taking into account my voxelized source image? Apart from that, I've simulated a simplified geometry, directly defined in GATE with no voxelized input, and that worked very well.

  *   Right there another question arose: How can I visualize the source? I found the command: /gate/source/[Source name]/visualize count color size
I double checked my geometry and source position with that command and both seem to be nicely centered at the isocenter (see the image below). As you can see, the source (in blue) is of spherical shape instead of my patient anatomy's shape. And am I not deforming the source when I change its size with this command? Is it possible to visualize both, voxelized geometry and voxelized source to check position and alignment? Of course, as my voxelized source is not working, the source in the image is just the mistakenly simulated point source... By the way, is it possible to visualize the CT image? I found in the documentation, that the immediate viewer (OGLI) should be able to visualize "cut-through-slices", but unfortunately, this viewer is not working in the virtual gate machine...

[cid:image004.jpg at 01D4F609.B4EA75B0]

  *   Last question: Is it possible, that the imageReader when loading an interfile image, loads the slice thickness in pixel instead of the size of z in mm? I noticed that, when I checked the size of my geometry and source. I had to copy the value of z into the slice thickness part in my interfile header and only then got the right geometry and source size.

I hope this description of my problem becomes clear. If not, please let me know, such that I can provide further information!

Many thanks in advance for all your help, comments, suggestions and time! And thanks at this point to those who did provide examples on the opencollaboration webpage, they were very helpful to get started!

Best,
Julia
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