[Gate-users] Mean energy vs. Radial distance in Elekta Precise 6MV phase-space data

[Stathis Kamperis]

Indeed, without knowledge of the geometry it's just guessing. I will
try also with different linac heads (e.g., varian or siemens just out
of curiosity and will post my results to the mailing list for
archiving purposes).

Many many thanks.

-Stathis

On Mon, May 12, 2014 at 4:15 PM, Grevillot Loic
<loic.grevillot at medaustron.at> wrote:
> I do not see any reason for that peak of mean energy.
> Actually the main issue is that you do not know which geometry was accounted for to generate the IAEA phase space, therefore it is quite complicated to conclude.
> In my paper, there is not such a peak of mean energy. There is a peak of Fluence however, due to the end of filter material.
> Hope this help.
> Sincerely,
> Loic
>
> -----Original Message-----
> From: Stathis Kamperis [mailto:ekamperi at gmail.com]
> Sent: Montag, 12. Mai 2014 14:55
> To: Grevillot Loic
> Cc: gate-users
> Subject: Re: [Gate-users] Mean energy vs. Radial distance in Elekta Precise 6MV phase-space data
>
> On Mon, May 12, 2014 at 11:40 AM, Grevillot Loic <loic.grevillot at medaustron.at> wrote:
>> Hi Stathis,
>>
> Hi Loïc and thank you for being so kind as to answer my questions!
>
>>
>>
>> What you should observed is the following:
>>
>> -          At the center: a higher energy and a lower fluence due to the
>> filter thickness
>>
>> -          With increased radial distance: a reduced mean energy and
>> increased fluence
>>
>> -          At the filter border: you suddenly have no filter material, so
>> the fluence increases and the mean energy decrease.
>>
>
> Indeed, all these make sense. As thickness increases, fluence decreases due to attenuation and mean energy increases due to beam hardening.
>
> What puzzled me the most though, was the sudden peak of mean energy near the flattening's filter edge. I was expecting the curve to decrease monotonically.
>
> I double checked my graph (with R and Mathematica) by looking at ~1.5 x 10^6 photons. The peak is always there.
>
> I have a theory, but this is just a theory :)
>
> http://dl.dropboxusercontent.com/u/25202446/peak-theory.png
>
>> Actually, what happens at the border of the filter is not important,
>> in the sense that this part of the beam is not use clinically.
>>
>
> Indeed. I was just curious from a purely scientific point of view :)
>
> Thank you again!
>
> Best regards,
> Stathis
>
>>
>>
>> Sincerely,
>>
>>
>>
>> Loïc
>>
>>
>>
>>
>>
>>
>>
>> From: gate-users-bounces at lists.opengatecollaboration.org
>> [mailto:gate-users-bounces at lists.opengatecollaboration.org] On Behalf
>> Of Stathis Kamperis
>> Sent: Freitag, 9. Mai 2014 19:15
>> To: gate-users
>> Subject: Re: [Gate-users] Mean energy vs. Radial distance in Elekta
>> Precise 6MV phase-space data
>>
>>
>>
>>
>> Στις 9 Μαϊ 2014 10:28 π.μ., ο χρήστης "Stathis Kamperis"
>> <ekamperi at gmail.com> έγραψε:
>>>
>>> Hello everyone,
>>>
>>> I'm using the Elekta Precise 6MV phase space data from the site of
>>> IAEA. I was plotting the mean photons' energy vs. radial distance and
>>> there's a peak around ~6-7.5cm that I cannot explain:
>>>
>>> http://dl.dropboxusercontent.com/u/25202446/peak.png
>>>
>>> Also, the graph from here
>>> http://www.creatis.insa-lyon.fr/~dsarrut/articles/Grevillot2011.pdf
>>> lacks such a peak (not sure if it is the same exact linac model).
>>>
>>> The closest clue I could get is from Grevillot et al:
>>>
>>> "... step in the particle radial fluence is observed between 65 and 70
>>> mm in (b), corresponding to interactions of the photons with the flat
>>> bottom edge of the flattening filter."
>>>
>>> Do you have any suggestion on how to interpret my results ? Perhaps
>>> the simulation of the IAEA phase-space data used a smaller flattening
>>> filter ? And too many photons pass through its edge ?
>>
>> Actually that doesnt make sense. We are plotting mean energy, not fluence.
>>
>> (I think that
>>> the plot code is correct, since it uses the fields package of R.)
>>>
>>> Thank you for your consideration,
>>>
>>> Best regards,
>>> Stathis
>>
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