[Gate-users] Positron Dosimetry Validation Questions

Wed Aug 24 17:31:05 CEST 2022

Hi all

I'm just looking for a little inspiration at the moment as I'm going around in circles a little. I tried to validate my PET-CT dosimetry macro by attaching a few TLDs to the outside of a hot filled NEMA phantom but unfortunately when I simulate with positron emissions, I end up a couple of orders of magnitude high (~2mGy instead of ~0.02mGy). As the TLDs are attached directly to the phantom, but I wasn't sure of the impact of the positrons themselves, I tried simulating just back-to-back gammas and this reduced the dose by around 50%, it is still too high. I ran the simulations for 32M events and then scaled this by the cumulated activity in the NEMA phantom. I trust the code more than I trust my calibration of the TLDs in a mixed positron/gamma environment to be honest though.

So instead, I thought I would try and replicate some of the SAF factors in ICRP 110, but I am struggling to see how I can utilise the DAT files. My best guess is to learn Python and then try and create an MHD file or similar from the DAT files but I'm not entirely sure if this is the best way to go about it. I can't find any reference that GATE can handle the DAT files directly. Before I go down that rabbit hole, I thought I would ask the community rather than reinventing the wheel.

How has anyone else validated their dosimetry code? Has anyone successful used TLDs for positrons and gammas? Is the best approach to utilise the DAT files instead, and what is the simplest method for that?

Thank you in advance

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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