[Gate-users] positron range

[Marlen Priegnitz]

Dear Nicolas Karakatsanis,

I observed the same problem as described by JinSu Kim in his 1st question.
I was simulating a cylindrical water phantom (Rmax=90 mm, Rmin=25mm, 
Height=93 mm), filled with quite low activity of 0,08 Bq/mm3.
I tried different (voxelized) sources. For backtoback source everything 
is ok, but for positron source and also 11C-source I got the same warning:
[GateTrajectoryNavigator::FindAnnihilationGammasTrackID] WARNING : 
positron found and photonID vector size: 1
This occured very very often until finally I got:
Break: Segmentation violation.
And then nothing happend anymore. The program didn't stop but it also 
didn't do anything else.
Because I also read, this happens because of not annihilated positrons, 
I simulated a 5mm thick plastic cylinder around the water phantom. But 
nevertheless, I got these warning messages in a huge amount (less than 
without plastic, but still so many that the program broke down).

Maybe this can help a little bit in investigating this problem.

Marlen



Nicolas Karakatsanis wrote:
> Dear JinSu
>
> regarding your first question this is a warning message generated by 
> GATE in the following cases
> a) a positron was generated but no annihilation gamma photons were 
> produced. If your geometry around your source was not dense enough to 
> ensure annihilation of some emitted positrons then it is very likely 
> that this warning message will appear during GATE simulation. This 
> warning is repeated every time a trajectory with this properties is 
> processed by GATE trajectory navigator.
>
> b) a positron was generated and then either 1 or more than 2 
> annihilation gammas were produced. In most cases you would expect to 
> have two annihilation gammas. So this is unlikely to happen.
> In your case one gamma photon was generated after the positron. This 
> is strange for GATE trajectory navigator and we might need to 
> investigate it further.
> Please can you give us more details on this. For example, was this 
> warning message produced many times? What kind of source have you 
> used? What was the geometry of your phantoms?
> If you repeat the simulation with a thicker surrounding attenuation 
> volume, will you still get these warnings?
>
>
>
> As far as the second question is concerned the GATE developers 
> community has been investigating the methods used by GATE to calculate 
> positron range recently because we observed some strange results 
> regarding the positron annihilation distance. It is likely to have 
> discrepancies between literature and GATE.
> However we would like you to tell us how did you estimate the positron 
> range you mention.
> Is this question related to the same simulation that generated the 
> previous warning message?If not, then what kind of source have you 
> used and what was it's shape and dimensions.
> Moreover it will be helpful if you can tell us a little more about the 
> properties (shape, dimensions) of the water volume that surrounded 
> your source.
>
> Nicolas
>
> Nicolas Karakatsanis
> PhD Candidate
> School of Electrical and Computer Engineer
> National Technical University of Athens
>
>
> JinSu Kim wrote:
>>
>> Dear Gate users
>>
>> 1^st question is ..
>>
>> During gate simulation, I found following error message
>>
>> Is it negligible?
>>
>> [GateTrajectoryNavigator::FindAnnihilationGammasTrackID] WARNING : 
>> positron found and photonID vector size: 1
>>
>> 2^nd question is about the Positron range of F-18
>>
>> In the literature, positron range of F-18 was 0.2 mm at water
>>
>> However, I found that the positron range of F-18 was 0.43 mm at water 
>> in GATE simulation.
>>
>> What is the difference of that?
>>
>> Best regards
>>
>>
>>
>> __________ NOD32 2680 (20071123) Information __________
>>
>> This message was checked by NOD32 antivirus system.
>> http://www.eset.com
>> ------------------------------------------------------------------------
>>
>> _______________________________________________
>> Gate-users mailing list
>> Gate-users at lists.healthgrid.org
>> http://lists.healthgrid.org/mailman/listinfo/gate-users
>>
>>
>>
>> __________ NOD32 2680 (20071123) Information __________
>>
>> This message was checked by NOD32 antivirus system.
>> http://www.eset.com
>>   
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> Gate-users mailing list
> Gate-users at lists.healthgrid.org
> http://lists.healthgrid.org/mailman/listinfo/gate-users
>