[Gate-users] Dose Calculation interface problem?

[Grevillot Loic]

Hello,

I would suggest you to try the latest Gate release, to start with some example and complexify them step by step to understand what happens.
In addition, I would suggest to use steps and cuts always lower than the scoring resolution.

Loïc

From: Gate-users [mailto:gate-users-bounces at lists.opengatecollaboration.org] On Behalf Of Theodora Kostou
Sent: Friday, August 11, 2017 12:04 PM
To: gate-users at lists.opengatecollaboration.org
Subject: [Gate-users] Dose Calculation interface problem?


Dear GATE users,

I am trying to use GATE to calculate the effect of a nanoparticle on the depth-dose curve in radiation therapy. As I was getting incorrect results, I scaled up the problem in order to eliminate possible nano-effects. However, even at the mm level, the problem still persists.

It seems to me that there is a problem with geometrical interfaces. Any help would be appreciated.

Here is the setup:

The phantom is a box of water, 20x20x20 mm3 in size. It is irradiated by a 2x2 mm2 square source emitting monoenergetic 140.5 keV photons, placed 2 mm outside the phantom (The small sizes of the phantom and the source are necessary in order to achieve good statistics when a nanoparticle is inserted in the phantom). Dose is scored in a 200x200x200 matrix. Each voxel is 0.1x0.1x0.1 mm3.

Then, I add a 2mm thick layer of water, placed 5 mm below the surface of the phantom, i.e inside the phantom. The depth-dose curve now exhibits two sharp peaks at the location of the interfaces of the water layer and the water phantom (at 4 and 6 mm).

The simulations were run on the VIP platform using GATE v6.2. To narrow down the causes I turned off all physical processes, except the Compton effect.

Since physically nothing has changed - we are still dealing with a cube of water - I suspect that the cause of the problem is the mere introduction of a new geometrical volume.

Has anyone ever encountered this problem? What are the solutions?

Thank you,
Theodora

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