[Gate-users] Problem using the HounsfieldMaterialGenerator while applying custom ionisation potentials

Fri Mar 17 17:41:27 CET 2017

Hi Loic,

Thanks for the email.  I've figured out a temporary workaround which I think should do the trick - although it's not elegant and not integrated into Gate.  Once I've done some testing I'll try downloading the code to Gate and see if I can figure out a better way to do it so that it integrates properly.

Thanks,
Adam

From: Grevillot Loic [mailto:loic.grevillot at medaustron.at]
Sent: 17 March 2017 15:45
To: Aitkenhead Adam (RBV) NHS Christie Tr; gate-users at lists.opengatecollaboration.org
Subject: RE: [Gate-users] Problem using the HounsfieldMaterialGenerator while applying custom ionisation potentials

Hello Adam,

Thank you for raising this point.
We should have a look in the code - I put this issue in my todo list (which is too big already :)) - so I encourage you to investigate the code on your side! You could create a bug report on the github and work on a separate branch to propose a bug fixing. We could integrate your corrections in the next release after validation.
Information on how to access github, etc. shall be available in the signature below.
Cheers,
Loïc

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From: Gate-users [mailto:gate-users-bounces at lists.opengatecollaboration.org] On Behalf Of Aitkenhead Adam (RBV) NHS Christie Tr
Sent: Thursday, March 16, 2017 5:26 PM
To: gate-users at lists.opengatecollaboration.org<mailto:gate-users at lists.opengatecollaboration.org>
Subject: [Gate-users] Problem using the HounsfieldMaterialGenerator while applying custom ionisation potentials

Hi,

I'm having difficulty applying custom ionisation potentials while using the HounsfieldMaterialGenerator in Gate 7.2.  The underlying problem is that custom ionisation potentials for elements don't seem to be inherited by subsequent materials.

For example: In Gate 7.2 the default ionisation potential for oxygen is 95 eV.  If I would prefer to use the potential (106 eV) listed in ICRU report 49, then I can set this as follows:

/gate/geometry/setIonisationPotential Oxygen 106 eV

The problem is that this new ionisation potential value is not used by Gate when it uses the Bragg additivity rule to calculate the ionisation potential for any materials containing oxygen.  For example, the ionisation potential of water remains at 68.998 eV, instead of increasing to 75.3 eV.

This isn't a problem for simple geometric simulations where a small number of materials are used, as the ionisation potentials for each material can be individually specified.  E.g.:

/gate/geometry/setIonisationPotential Water 75.3 eV

However, it is a problem when a simulation uses a CT image and materials are generated using the HounsfieldMaterialGenerator.  In this case, ionisation potentials are calculated based on the default element ionisation potentials - regardless of any custom element ionisation potentials that have been defined.

Does anyone have any suggestions - either for something I might have misunderstood, or for a workaround to allow custom ionisation potentials to be applied while using the HounsfieldMaterialGenerator?

Thanks,

Adam

adam.aitkenhead at christie.nhs.uk<mailto:adam.aitkenhead at christie.nhs.uk>
Christie Medical Physics & Engineering

The Christie NHS Foundation Trust
Manchester, UK

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