[Gate-users] Edep returned by DoseActor is about 7 times bigger then hand calculated value

[Grevillot Loic]

FYI,
DoseActor validation tests were provided for the GATE-RTiON<https://gate.uca.fr/download/gate-rtion> release, in the context of light ion beam therapy under the gitcontrib<https://github.com/OpenGATE/GateContrib/tree/master/GATE-RTion> repository.
The tests can be applied in principle to any GATE release and may help you as a starting point.
It would be nice to increase the collection of tests for other clinical applications such as  yours!

Best,
Loïc



From: Gate-users [mailto:gate-users-bounces at lists.opengatecollaboration.org] On Behalf Of Albert Grace Lieu
Sent: Freitag, 5. März 2021 05:59
To: gate-users <gate-users at lists.opengatecollaboration.org>
Subject: [Gate-users] Edep returned by DoseActor is about 7 times bigger then hand calculated value

Hi Gate users,

I am validating the validity of DoseActor in GATE for radionuclide dosimetry application. Surprisingly, I found the Edep returned by DoseActor is about 7 times bigger than my hand calculated value, so does the dose returned by DoseActor. I could be wrong, but I double-checked everything I did and had been as prudent as I can before asking for suggestions here.

Here is what I did in GATE:

  *   Phantom: 101*101*101 voxelized tissue ( water equivalent) phantom, with a side of 2 mm for each voxel
  *   Source: 10 mm radius sphere voxelized Lu177 source with a side of 2 mm for each voxel, and being placed in the center of the phantom
  *   DoseActor: record dose, Edep, and export a mass image of the phantom (all 3D array)
  *   ProductionAndStoppingActor: record the number of Lu177 generated in each voxel, indicated by Lu177-Stop (3D array)
        According to the user manual, "The unit of edep is MeV and the unit of dose is Gy".

Here is how I calculate the average of the energy of Lu177 in water, Lu177 is a beta emitter, the range of electron in water is way smaller than 2mm, thus it is stopped where is created. Given the branching ratio of Lu177, on average a single Lu177 disintegration would deposit 134.16 Kev (electrons only) or 162.95 Kev (electrons and gammas).

[RTEmagicC_Lu-177_decays.png.png]

However, when I divide Edep by Lu177-Stop, the energy per Lu177 disintegration returned by DoseActor is ~1.0 Mev, which 7 times bigger than my hand calculated value. Is this an internal issue? I attach my Gate code for your review.


Thanks a lot for your help.
Sincere wishes,
Stay safe and healthy
Albert


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