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

[Grevillot Loic]

Hi Stathis,

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.
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.

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<mailto: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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