[Gate-users] DoseActor output: unexpected absorbed dose values

[Francesca De Benetti]

Dear GATE users,

I am using GATE to simulate the absorbed dose in internal radiotherapy applications. The voxelized geometry consists in an abdominal CT and the voxelized source is a SPECT. The two volumes have the same size and the same resolution. The SPECT is loaded using the linear translator. Doing several simulations I noticed two issues I can’t understand in the dose returned as output by the DoseActor. 

If I run the simulation on the whole CT and the whole SPECT (242x223x42), I get as maximum value 0.0132 Gy. If I run the very same simulation on a crop of the previous CT and the corresponding crop of the previous SPECT (16x16x4), the maximum value is 5.3849 Gy. The resolution of the DoseActor is the same as the CT, and its size is the size of the CT (respectively 242x223x42 and 16x16x4). What can be the reason of this huge difference?
I also tried to run simulations on the crops with and without padding the SPECT. Here the set up is: a CT crop (16x16x4) and a SPECT crop (12x12x2). The first simulation uses the two original crops, whereas the second simulation uses a zero-padded SPECT (with final size 16x16x4). In both cases the DoseActor has the same size and resolution of the CT. However, the output doses are not equivalent. I expected the zero-padding to have no effect, but apparently that is not the case. Do you have any suggestion? Checking the difference between the two volumes, it doesn’t seem an alignment problem between the source and the CT.

Please, let me know if you need some more details! 
Thank you in advance to everyone who will help me! 


Best regards,
Francesca De Benetti
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