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

[Stathis Kamperis]

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 ? (I think that
the plot code is correct, since it uses the fields package of R.)

Thank you for your consideration,

Best regards,
Stathis