[Gate-users] LET Actor Giving Strange Results?

[Andreas Resch]

Hi Cassandra,

LETt,d is an averaged value, so summing it along one dimension if you score
a 3D map is not the same as scoring a 1D map. So the two curves should not
look the same.

There is the option "doParallelCalculation"  giving you the numerator and
denominator separately. If you sum those up individually and afterwards do
the division you should end up in the same result as the 1D output. See
also here:
https://opengate.readthedocs.io/en/latest/tools_to_interact_with_the_simulation_actors.html#let-actor
note that the denominator is actually the dose distribution in your case.

cheers,
Andreas

Am Mo., 15. März 2021 um 20:45 Uhr schrieb Cassandra Miller <
cassandramiller at phas.ubc.ca>:

> Hi everyone,
>
> I'm trying to do some calculations using the LET actor but my results
> don't match when I think they should.
>
> I created a water density box (1x3x1 mm) with a point source of 500 keV
> beta particles at the top of the box in the y-direction. I used the LET
> actor as both a 3D matrix and an effectively 1D matrix, essentially like
> so:
>
> /gate/actor/addActor    LETActor       MyActor3D
> /gate/actor/MyActor3D/save               output/myLETactor3D.mhd
> /gate/actor/MyActor3D/attachTo           box
> /gate/actor/MyActor3D/setResolution     25 75 25
> /gate/actor/MyActor3D/setType            DoseAveraged
>
> /gate/actor/addActor    LETActor       MyActor1D
> /gate/actor/MyActor1D/save               output/myLETactor.mhd
> /gate/actor/MyActor1D/attachTo           box
> /gate/actor/MyActor1D/setResolution      1 75 1
> /gate/actor/MyActor1D/setType            DoseAveraged
>
> I would expect the output to look similar, and the 3D matrix to exactly
> match the 1D matrix when I sum it in the x and z direction, to change
> its shape to (1, 75, 1) so they are the exact same shape.
>
> I get the attached images which don't look the same at all. They're not
> even the same shape. Does anyone know why this is? Does changing the
> resolution change something else I'm not aware of? I also tried using
> the command "/gate/actor/MyActor1D/setVoxelSize      1 0.04 1 mm" to
> make sure my 1D actor was capturing the entire box, but the shape still
> didn't match.
>
> Best,
> Cassandra
>
> --
>
> Cassandra Miller
> PhD Candidate, Physics
> Quantitative Radiomolecular Imaging and Therapy Lab
> Department of Physics and Astronomy, University of British Columbia
>
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