[Gate-users] Questions on Dose Actors

[Nada Fakhoury]

Dear Gaters,

I have some questions on how the dose actors actually work.

In the case of a Radiotherapy Simulation, let's assume we have a water  
phantom of 50x50x50 cm and we attach to it the Dose actor with a  
resolution of 1 1 500, at the center of the volume. That would mean  
that the dose is calculated in voxels with a size 500 500 1 mm. So  
that essentially means that dose is calculated by layers of the entire  
phantom, am I right?

And in the case of attaching the same actor to calculate a dose  
profile on the x axis at various depths, if for example it is attached  
at z=10 cm depth and the voxel size is now 1 500 500 mm, won't the  
voxel dimensions exceed the volume boarders in the z direction on one  
side?

I am puzzled by the above, by the fact that when acquiring dose  
profile in various depths the seem to me perfectly fine, as they do  
present a dose reduction by depth. But when I think of the voxel size,  
I am troubled.

Now, for precision's sake I know that I can alter the voxel size and  
attach the dose actor exactly where I want.

But my current goal is to validate my geometry with dosimetric data.  
And the question is whether I can or cannot use the dose actor as  
stated in the begging. And that is for two reasons. My dosimetry data  
was taken with an ion chamber, which means that it was taken with a  
specific voxel size. But if I wish to make a simulation with a much  
smaller voxel size than the one I've been using so far, that would  
mean I'd have to use way more primary particles than I already do. But  
since I am only running GATE on my laptop, I don't have the  
computational capacity to run with too many particles.

So should dosimetric data be compared with dose calculated with a 1 1  
500 resolution , just for the sake of validating a geometry and a  
source's energy?

Cheers,
Nada
-- 
Nada Fakhoury
MSc "Medical Physics" Student