[Gate-users] LET Actor Giving Strange Results?

[Konstantinos P. Chatzipapas]

Hello Cassandra,
You can also check this article (https://www.nature.com/articles/s41598-019-56258-5.pdf?proof=t) to understand exactly what is different in the calculation of LET using the 'Dose Average' method.e.g.: "The LET from each particle is weighted with respect to its contribution to the local dose in each voxel"
Kind regards,Konstantinos
----------------------------------------------------- Konstantinos Chatzipapas
    Medical Physicist, MSc
       University of Patras
 web: Physics Magazine 

    Στις Τρίτη, 16 Μαρτίου 2021, 10:24:36 π.μ. EET, ο χρήστης Andreas Resch <resch.andi at gmail.com> έγραψε:  
 
 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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