[Gate-users] positron range

[JinSu Kim]

Dear Nicolas and Gate users

 

Regarding Positron range

I have used Fluorine-18 source for simulation (ion 9 18 0 0)

 

Phantom

Geometry ~ diameter: 6 cm & Length: 15 cm

Material ~ water

 

Source 

Shape and dimension of fluorine-18 ~ 1) point source & 2) length 15 cm and
diameter 0.1 cm

 

I have addressed that the positron range of F-18 was 0.43 mm in my
simulation result

That is mean value. Maximum value of positron range was near 2 mm.

As I have mentioned the reference value of positron range of F-18 was 0.2 mm
(mean value)

 

Another question is regarding warning message.

Following warning message
"[GateTrajectoryNavigator::FindAnnihilationGammasTrackID]  WARNING :
positron found and photonID vector size: 1 " 

were occurred in different simulation study

That occurred in many times

However, the result of simulation was reasonable compared with the measured
value.

 

Best regards

 

JinSu Kim

 

  _____  

From: Nicolas Karakatsanis [mailto:knicolas at mail.ntua.gr] 
Sent: Friday, November 23, 2007 9:22 PM
To: JinSu Kim; gate-users at lists.healthgrid.org
Subject: Re: [Gate-users] positron range

 

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

 

1st question is ..

During gate simulation, I found following error message

Is it negligible?

[GateTrajectoryNavigator::FindAnnihilationGammasTrackID]  WARNING : positron
found and photonID vector size: 1

 

2nd 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

 

 

 

 

 



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