<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="6.x">Drupal-Biblio</source-app><ref-type>47</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Vidal, M.</style></author><author><style face="normal" font="default" size="100%">De  Marzi,  L.</style></author><author><style face="normal" font="default" size="100%">Szymanowski, H.</style></author><author><style face="normal" font="default" size="100%">Nauraye, C.</style></author><author><style face="normal" font="default" size="100%">Hierso,  E.</style></author><author><style face="normal" font="default" size="100%">Freud, N.</style></author><author><style face="normal" font="default" size="100%">François, P.</style></author><author><style face="normal" font="default" size="100%">Sarrut, D.</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">How to minimize and model the collimator scatter in Double Scattering  and  Uniform  Scanning.</style></title><secondary-title><style face="normal" font="default" size="100%">Particle Therapy CoOperative Group (PTCOG 50)</style></secondary-title></titles><dates><year><style  face="normal" font="default" size="100%">2011</style></year><pub-dates><date><style  face="normal" font="default" size="100%">05/2011</style></date></pub-dates></dates><urls><related-urls><url><style face="normal" font="default" size="100%">http://www.creatis.insa-lyon.fr/site/sites/default/files/Poster_PTCOG50.pdf</style></url></related-urls></urls><pub-location><style face="normal" font="default" size="100%">Philadelphia, PA, USA</style></pub-location><abstract><style face="normal" font="default" size="100%">Introduction: 
Collimators  are  commonly  used  as  lateral  beam  shaping  devices  in  proton  therapy  with 
passive scattering (Double Scattering DS) and Uniform Scanning (US) beam lines. The dose 
contamination due to collimator scattering can reach up to 10 % of the maximum dose for a 
Spread Out Bragg Peak dose distribution. The aim of this study is to characterize and model 
the aperture contamination. 
 
Material and Methods: 
The  new  analytical  model  describes  the  collimator  scatter  distribution  as  a  3D  function  of 
depth and of the transverse coordinates, and treats separately the two different contamination 
components emerging respectively from the inner and the entrance faces of the collimator. 
Measurements  were  performed  at  CPO  (Orsay,  France)  with  a  230  MeV  IBA  beam  line  in 
DS,  with  divergent  apertures,  for  several  field  sizes  and  energies.  Monte  Carlo  simulations 
were run on the platform GATE based on Geant4. 
 
Results: 
Comparisons were performed against measurements in presence of collimators and show an 
excellent agreement. Maximal dose deviations up to 1.5% relative to the maximum dose were 
observed for the entrance face component. More clinical configurations were simulated with 
the validated Monte Carlo code and the analytical model agrees within 0.5% ± 0.1%. 
 
Conclusion and perspectives:  
The collimator scatter is well predicted with the developed fast analytical algorithm and will 
be used to improve Monitor Units calculation. A study comparing dose contamination using 
divergent or non-divergent apertures is still on-going. As good results were obtained for DS, 
work about the possible use of this  model is in progress for the Uniform Scanning delivery 
technique. </style></abstract></record></records></xml>