[Gate-users] Three problems with Gate 6.1

[Nikolaos A. Karakatsanis]

Dear Min-Jae,

after conducting an evaluation study to access positron range modeling 
in GATE for different types of point sources and material distributions 
surrounding the source, I confirmed that, indeed, multiple local minimum 
are present in the positron range histogram when a single attenuating 
medium surrounds the point source.

However, I discovered a temporary, but efficient and simple, workaround 
for this issue that can allow you to reliably calculate positron range 
of any radio-isotope in any material supported by GATE.

The proposed solution involves the addition of a volume (sphere, 
cylinder, etc) of Air of nearly-zero dimensions, which completely 
surrounds the studied point source. Beyond that thin air layer, you can 
add any other surrounding attenuating volume, such as water, breast, 
skull, etc to investigate the positron range.

It is important to choose a very thin (I have chosen 0.01mm, but maybe 
you can try even smaller orders of magnitude)  layer of air, because 
thicker layers may bias your positron range calculation. Nearly all 
positrons emitted by the radio-isotopes in medical imaging have 
sufficient kinetic energy to go through thin layers of air without 
annihilating or without even losing significant fraction of their 
initial kinetic energy.

Once again, thank you for bringing this into the GATE community's 
attention. This issue remains, to my knowledge, unsolved, and we will 
have to go through it very soon.

Please report us back if the proposed source-phantom configuration does 
not work for any of the sources or material distributions examined in 
terms of positron range.

Best regards,
Nicolas

____________________________________________________
Nikolaos A. Karakatsanis, PhD
Division of Nuclear Medicine
Department of Radiology
Johns Hopkins Medical Institutions
Room 3263, JHOC Bldg
601 N. Caroline Street
Baltimore, MD, USA, 21287


On 7/7/11 10:52 AM, MinJae Park wrote:
> Dear Nikolaos,
>
> I use two sphere of water phantom as your post.
> 1. radius : 0~0.01mm
> 2. radius : 0.011mm~20cm
> Source is in the sphere #1.
>
> However, I couldn't choose physical model for low energy at this
> moment because of "COMMAND NOT FOUND".
>
> Therefore, the result, which I got, could be wrong.
>
> I will post the result after using physical model for low energy.
>
> Thank you,
> MJ
>
> //=================================================
> //  MinJae Park, Ph.D.
> //
> //  Johns Hopkins University
> //  School of Medicine, Dept of Radiology
> //  Division of Medical Imaging Physics
> //
> //  DialTo:+1-443-287-2005 (Office)
> //  MailTo:MJ at ToTi.us, MJ at JHMI.edu
> //
> //  "You see, But you do not Observe"  - Sherlock Holmes -
> //=================================================
>
>
>
> On Wed, Jul 6, 2011 at 6:37 PM, Nikolaos A. Karakatsanis
> <nkaraka2 at jhmi.edu>  wrote:
>> Dear Min-Jae,
>>
>> thank you for reporting this potential problem in GATE.
>>
>> I personally had come up with this suspicious behavior in the past too.
>> After conducting a validation study using different materials and sizes for
>> the source and the attenuating medium, I concluded that the problem is
>> related with the set-up of source-medium employed to access positron range.
>>
>> The distance corresponding to the local minimum observed between the two
>> peaks of the positron range is strongly related with the distance of the
>> outer boundary of the source from the center of the source. In other words,
>> the local minimum is observed almost exactly at the interface between the
>> source and the surrounding attenuating material.
>>
>> I would suggest you not to use different materials for the source and the
>> attenuating volume. You can use water for both volumes, which is a very
>> realistic set-up to access positron range.
>>
>> However, even if the problem is eliminated, the behavior you report is
>> suspicious and probably we need to go through the implementation of the
>> physical processes in GATE and Geant4.
>>
>> To assist us, please attach the positron range spectrum after using GATE 6.1
>> and GATE 5 and kindly provide us with a description of the materials and the
>> geometry of source and attenuating medium that you have been using
>>
>> thank you.
>> Nicolas
>>
>> ____________________________________________________
>> Nikolaos A. Karakatsanis, PhD
>> Division of Nuclear Medicine
>> Department of Radiology
>> Johns Hopkins Medical Institutions
>> Room 3263, JHOC Bldg
>> 601 N. Caroline Street
>> Baltimore, MD, USA, 21287
>>
>>
>> On 7/6/11 5:52 PM, MinJae Park wrote:
>>> Dear Gaters,
>>>
>>> Recently, I installed Gate 6.1 to investigate the positron range of Rb-82.
>>>
>>> But, I can't use different physical model using "setModel" command.
>>> I got an error as below when I tried to use setModel.
>>> [G4-cerr] ***** COMMAND NOT FOUND
>>> </gate/physics/processes/ElectronIonisation/setModel PenelopeModel e+>
>>> *****
>>>
>>>
>>> In addition, since the positron range was deactivated by default,
>>> I modified the source code to get the positron range.
>>>
>>> However, even though ion source (37 82 0 0) was used,
>>> the positron range was little bit different from Gate 5.0 and
>>> also from the reference paper (Levin, Calculation of positron
>>> range..., PMB, 1999).
>>>
>>> I guess this might be a problem with physical model at low energy.
>>>
>>>
>>> One more, I can't use parameterization on batch mode.
>>> For example, "Gate -a nZ 37 -a nA 82<    sim.mac".
>>> "Gate -a nZ 37 -a nA 82 sim.mac" is working, though.
>>>
>>>
>>> Thank you,
>>> MJ
>>>
>>> //=================================================
>>> //  MinJae Park, Ph.D.
>>> //
>>> //  Johns Hopkins University
>>> //  School of Medicine, Dept of Radiology
>>> //  Division of Medical Imaging Physics
>>> //
>>> //  DialTo:+1-443-287-2005 (Office)
>>> //  MailTo:MJ at ToTi.us, MJ at JHMI.edu
>>> //
>>> //  "You see, But you do not Observe"  - Sherlock Holmes -
>>> //=================================================
>>> _______________________________________________
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