[Gate-users] Odd Results between Positron and Gamma Simulations in Digimouse data

[BAKER, Mark (THE CLATTERBRIDGE CANCER CENTRE NHS FOUNDATION TRUST)]

Hi all

I've been working on some basic simulations using the digimouse data, whereby I have masked organs on the PET data based on the atlas and then run simulations. My initial simulation used positrons as the source, virtually all of the hits (and dose) was in the organ of interest (example of the heart simulation is attached). I wasn't confident that the distal organs would receive so little from the generated 511keVs, so I thought I'd run a just a back to back gamma version to remove the positron component. Both simulations were 1 million events (so obviously there would be a branching ratio difference) but shouldn't be too far different. However, this generated a weird artefact which looks like a cylinder of hits, as shown in the gamma_mouse image attached. I'm at a loss as to why the simulation ended up like this. The NbofHits, edep actors etc. also show the same effect.

I've attached both the physics and source macs I used, with the source mac showing both the positron and gamma sections (which I just switch between commented).

Any help would be great! I'm struggling to receive emails from the list at the moment (nothing since August), so I think it might be better to email me back directly but probably leave the mailbase still copied in.

Thank you

Mark Baker
Principal Clinical Scientist
Imaging Physics (Ionising)
The Clatterbridge Cancer Centre NHS Foundation Trust
(he, him)

CCCW Tel:  0151 556 5030
CCCL Tel: 0151 318 8438
Email: mark.baker23 at nhs.net<mailto:mark.baker23 at nhs.net>
Microsoft Teams (click here)<https://teams.microsoft.com/l/chat/0/0?users=mark.baker23@nhs.net>

Honorary Lecturer, Dept. of Physics
University of Liverpool

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