[Gate-users] 2D dose distribution on film dosimeters

[Andreas Resch]

Hi Sonja,

I have not tried to simulate films, but generally your step limiter 
should be lower than your scoring voxel size (and to avoid artifacts, I 
would also suggest using a step limiter which is n times smaller than 
your voxel size, where n is an integer and not a real number). As far as 
I know, a step in Geant4 is either limited by a geometrical boundary, 
step limiter or physical process. In the Bragg peak, I observed steps 
mostly being limited by physical processes, whereas in the entrance 
plateau it is limited by the step limiter or geometrical boundaries when 
you use a voxelized geometry. In your case, your maximum step size would 
be roughly 30 um if your active layer is inside of a geometrical box 
with thickness 30 um and the maximum step limiter is greater than 30 um. 
Note that a scoring grid (defined in the "actor") in Gate does not make 
a geometrical boundary in the simulation. You can define individual step 
limiters to several geometries:

/gate/physics/SetMaxStepSizeInRegion world 1 mm
/gate/physics/SetMaxStepSizeInRegion myPhantom 100 um

(usually higher accuracy with lower step limiter, but also increased 
computation time)

You can check the step lengths e.g. with the phase space actor.

cheers,
Andreas

Am 2016-12-16 12:29, schrieb Schellhammer, Sonja:
> Hi fellow simulators,
> 
> I'm modelling the expected 2D dose distribution of a proton beam on
> the active layer of a EBT3 film dosimeter. Does anyone have experience
> with this? I am a bit worried whether I can choose maximum step
> lengths and production cutoffs greater than the thickness of the layer
> (my scorer is as thick as the active layer, which is 30 microns).
> 
> Thanks for your ideas!
> Sonja

-- 
-------------------------

ANDREAS RESCH, M.SC.
PhD student, Medical Physics

MEDICAL UNIVERSITY OF VIENNA
Department of Radiotherapy
Christian Doppler Laboratory for Medical Radiation Physics for Radiation
Oncology

Waehringer Guertel 18-20, 1090 Wien
Ph: +43 (0)1 40400-72710
Ph: +43 (0)2622 26100-931
andreas.resch at meduniwien.ac.at
www.meduniwien.ac.at/radonc