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

[Albert Grace Lieu]

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).

[image: 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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