[Gate-users] Fixed Forced Detection Actor: bugs concerning the choice of the source

[Simon Rit]

Hi,
Thanks for pointing this out. The scatter images should be accurate but the
primary image are indeed wrong (and I understand it's probably useless to
have the scatter images without primary).
For the point source, you should get a warning letting you know of this:
https://github.com/OpenGATE/Gate/blob/develop/source/digits_hits/src/GateFixedForcedDetectionActor.cc#L1490
We will add a check on the shape of the source to allow only rectangular
shapes.
If you need those sources, you can correct the code to account for these
source types, the problem should be handled in the PrimaryFluenceWeighting
function.
Simon

On Fri, May 5, 2017 at 3:06 PM, Triltsch, Nicolas <nicolas.triltsch at tum.de>
wrote:

> Hello Gate fellows,
>
> I noticed some bugs concerning the choice of the source when using the
> Fixed Forced Detection Actor (FFDA). As I can remember, the FFDA needs a
> focused source spot to work properly. In the example folder of Gate, the
> source was chosen to be a rectangle and in this case the simulation works
> properly. However, if different source types are tested the simulation
> gives strange results.
>
> I tried two different source types: Firstly, I changed the shape of the
> source to be a circle and secondly, I took a point source. I will explain
> the bugs I could notice in both cases.
>
> *1) Focused circle source:* Primary image and flatfield give nan. The
> Compton and Rayleigh scatter images are calculated, but depend on the
> number of simulated photons as the can not be normalized by an appropriate
> flatfield of nan's.
>
> ---primary and flatfield---
>
> ---compton---
>
> ---rayleigh---
>
> *2) Point source:* The primary image seems correct. However, the scatter
> images can not be calculated correctly, as they show a scatter-to-flatfield
> ratio of 80% for Compton and 40% Rayleigh. These values are impossible in
> the given simulation setup where I expect scatter ratios of around 1-2% (as
> verified with the experiment). I noticed that the ratios depend on the
> number of simulated photons which shouldn't be the case after flatfield
> normalization.
>
> ---primary/ff---
>
> ---compton/ff---
>
> ---rayleigh/ff---
>
>
>
> *Conclusion: *It seems that the FFDA only works if the source is chosen
> to be a focused rectangle and is bugy if other source types (circle or
> point source, maybe other types) are given.
>
>
>
> * Can anyone comment on this behavior? *See the used scripts attached.
>
> Regards,
> Nico
>
> --
> B.Sc. Nicolas Triltsch
> Masterand
>
> Technische Universität München
> Physik-Department
> Lehrstuhl für Biomedizinische Physik E17
>
> James-Franck-Straße 1
> 85748 Garching b. München
>
> Tel: +49 89 289 12591 <+49%2089%2028912591>
> nicolas.triltsch at tum.dewww.e17.ph.tum.de
>
>
> _______________________________________________
> Gate-users mailing list
> Gate-users at lists.opengatecollaboration.org
> http://lists.opengatecollaboration.org/mailman/listinfo/gate-users
>
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