[Gate-users] Strange behavior of Gate_v3.1.1 and Gate_v3.1.2

[Georgi Gerganov]

Dear Developers,

We are concerned that there is something wrong with Gate_v3.1.2. We have
been running simulations for quite a long time using Gate_v3.1.1 and
recently we have installed the new version of Geant (v4.9.0_p01) and ROOT (
v5.14.00) together with Gate_v3.1.2. The results we obtain running the same
simulations as before, totally defer from each other. The simulation
parameters are as follows:

Cubic water phantom 30x30x30cm, not voxelized or voxelized in 1cm or
0.4cmcubic voxels, center in (0,0,0)
The source is in the center (0,0,0), slightly translated with 1e-7cm to
avoid setting up the source on the intersect between voxels
Source activity is 1e6 bq.
The simulation Run is 10s long.
We are using General Electric scanner.

We are interested in the total singles and coincidences produced by the
simulations. The number of singles we obtain from both versions match quite
well. But the problem is that the number coincidences (true scattered and
true unscattered) differ from each other by an order of magnitude, which in
our opinion is quite disturbing. Performing one and the same simulation
(with exactly the same mac files in exactly the same directory) with one and
the same initial random seeds gives a huge difference in the number of
coincidences, which obviously is statistically significant. An example is
shown below:

*** Gate_v3.1.1 ***
Phantom: WaterBox, 1.0cm Vox
Singles: 708469
Random Coins.: 109
True Unscattered Coins.: 27304
True Scattered Coins.: 17191
Total: 44604
Events: 9995991

*** Gate_v3.1.2 ***
Phantom: WaterBox, 1.0cm Vox
Singles: 717897
Random Coins.: 111
True Unscattered Coins.: 2497
True Scattered Coins.: 5355
Total: 7963
Events: 9998927

Some time ago we have also noticed 2 more problems, this time with
Gate_v3.1.1:

1) We have prepared simulation files (again we were interested in the number
of singles and coincidences produced). Running the simulation gave us a set
of results (let's call them 'Results1'). Then, changing ONLY the line:
/control/verbose 0
to:
/control/verbose 2
Gave us another set of results (let's call them 'Results2'). It was quite
interesting to find that Results1 had nothing in common with Results2. We
have retested this many times and everytime the 'anomaly' was observed. What
has the verbosity to do with the number of singles and coincidences produced
by one and the same simulation?

2) This problem is quite similar to the one mentioned above. This time the
ONLY thing we've changed in the mac files, was the name of the ROOT output
file. Again the two sets of results we obtained had nothing in common. This
was also retested many times. Investigating the 'anomaly' we found out that
the set of results we obtain each time depends on the length of the ROOT
output filename.

All of the problems above where observed on two different machines.

Has anyone noticed problems, similar to those above? Is there a version of
Gate that is known to be stable?
Any suggestions and support will be appreciated.

Georgi Gerganov & Yordan Madzhunkov
Bulgaria, Sofia University
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