[Gate-users] CAUTION when using ion source with Geant4 version 10.5.0!

[Calvert Nicholas (RBV) NHS Christie Tr]

Dear, Julia, All,

As a bit of closure, I believe this discrepancy was caused by the lack of Internal Conversion electrons being generated in Geant4 10.5.0 which was reported as a bug here: https://hypernews.slac.stanford.edu/HyperNews/geant4/get/emprocess/1522.html

I guess this explains why the discrepancy was not seen with Y-90?

Regards,
Nick

Nick Calvert, PhD
Senior Research Scientist,
The Christie NHS Foundation Trust,
Manchester,
M20 4BX



-----Original Message-----
Dear All,

With respect to the message from Gunjan Kayal (http://lists.opengatecollaboration.org/pipermail/gate-users/2019-September/011088.html) , we continued on some tests regarding different GEANT4 versions with the use of the ion source command in GATE.

We've tested three Geant4/Gate combinations:
Geant4 10.5.1 (Gate 8.2)

Geant4 10.5.0 (vGate 8.2)

Geant4 10.3.3 (vGate 8.0)


Two scenarios were simulated and the dose was scored with the DoseActor and the S value was calculated. The obtained S values were subsequently compared to the literature.

-          Unit density sphere of 60g (geometry and source defined in GATE)

-          Voxelized human phantom for simulation of kidney S value

This was done for three nuclides: Lutetium-177, Yttrium-90 and Iodine-131.

The tables below show the percentage deviation of the simulated S value with GATE compared to the literature:

Sphere simulation
Nuclide

Version

Deviation [%]

I-131

Geant4 10.5.1 (Gate 8.2)

0.9

Geant4 10.5.0 (vGate 8.2)

6.4

Geant4 10.3.3 (vGate 8.0)

1.0

Y-90

Geant4 10.5.1 (Gate 8.2)

-0.7

Geant4 10.5.0 (vGate 8.2)

-0.7

Geant4 10.3.3 (vGate 8.0)

-0.6

Lu-177

Geant4 10.5.1 (Gate 8.2)

1.2

Geant4 10.5.0 (vGate 8.2)

11.9

Geant4 10.3.3 (vGate 8.0)

1.2


Kidney simulation
Nuclide

Version

Deviation [%]

I-131

Geant4 10.5.1 (Gate 8.2)

-1.1

Geant4 10.5.0 (vGate 8.2)

3.8

Geant4 10.3.3 (vGate 8.0)

-1.2

Y-90

Geant4 10.5.1 (Gate 8.2)

1.8

Geant4 10.5.0 (vGate 8.2)

1.8

Geant4 10.3.3 (vGate 8.0)

1.8

Lu-177

Geant4 10.5.1 (Gate 8.2)

2.6

Geant4 10.5.0 (vGate 8.2)

12.5

Geant4 10.3.3 (vGate 8.0)

2.5


The finding that Geant4 version 10.5.0 is showing large discrepancies was already pointed out by Gunjan who was simulating a different scenario with Lu-177 dose point kernels. But it is interesting to see, that the deviation is varying for different nuclides. We assume that this finding is related to the different decay schemes of the three investigated nuclides. Unfortunately, we could not find a hint in the Geant4 release notes or in the Geant4 user forum where this deviation for Geant4 version 10.5.0 is coming from.

We therefore recommend NOT to use Geant4 version 10.5.0, when using the ion source command! And to remind you, the virtual GATE8.2 is installed with Geant4 10.5.0!

Any help to find out the reason for the discrepancies is highly welcome!

Best,
Julia
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