[Gate-users] Unanswered:

maikol salas ramirez mmsalas at gmail.com
Wed Aug 9 11:48:58 CEST 2017


Hi Niels

One way, or at least the way that I used to learn, was: create a voxel and
attach it to an specific voxel of your phantom, the active the option for
energy loss:
Energy spectrum

This actor builds four histograms: the initial kinetic energy of each track
(energySpectrum), the energy deposition per event (edepHisto), the energy
deposition per track (edepTrackHisto), the energy loss per track
(eLossHisto). These histograms are stored in a root file. They takes into
account the weight of particles. They are three commands to define the
boundaries and the binning of the energy spectrum and three commands to
define the boundaries and the binning of the energy loss histograms
(edepHisto, edepTrackHisto, eLossHisto).

/gate/actor/addActor  EnergySpectrumActor  *MyActor*
/gate/actor/*MyActor*/save  MyOutputFile.root
/gate/actor/*MyActor*/energySpectrum/setEmin 0 eV
/gate/actor/*MyActor*/energySpectrum/setEmax 10 GeV
/gate/actor/*MyActor*/energySpectrum/setNumberOfBins 200
/gate/actor/*MyActor*/energyLossHisto/setEmin 0 eV
/gate/actor/*MyActor*/energyLossHisto/setEmax 15 MeV
/gate/actor/*MyActor*/energyLossHisto/setNumberOfBins 120


You will get an energy deposit spectrum in this specif voxel, I did the
energy conversion and considering the voxel volume and material density,
manually I calculated the dose, then I get a factor for my dose image.
The reason for the factor is due to emission probabilities of the source
and other issue like time and activity. If you are already fixing the
activity you will get in your spectrum of deposit energy in one line
emission probability and in other energy deposited for time unit.

*For example for this par data:*
*Energy (MeV)    Probability*
*0,001                  0,550919*

*To get the Dose:*

*Dose[Gy-MBq/s] =
 0,550919*0,001[MeV]*10E6[eV/MeV]*1,602176487E-19[J/eV]*(1/m[kg])*1E6[MBq/Bq]*3,826[particles/Bq-s]*

This last number correspond to the emission probability of all the emission
of the radionuclide (gammas+betas+IC electrons+Auger Electron).
In your case if you use only photon annihilation the probability is 1,935,
but if your source include also a positron espectrum the factor is
2,908. *Please
check here in table 5.2:*
*http://www.nucleide.org/DDEP_WG/Nuclides/F-18_tables.pdf
<http://www.nucleide.org/DDEP_WG/Nuclides/F-18_tables.pdf>*

*BUT, if are using GATE source take into account:*

*/gate/source/NAME/gps/particle e+
/gate/source/NAME/gps/energytype Fluor18
/gate/source/NAME/setForcedUnstableFlag true
/gate/source/NAME/setForcedHalfLife 6586 s
*

*In the above example, more properties of fluorine-18 have been added by
using the helper keyword Fluor18 (see below): half-life and energy
distribution. Note that the branching ratios are not respected with this
kind of simulation because no decay is simulated, i.e. emission is 100%
positron. You may want to lower the activity by an appropriate factor to
take this better point into account.*

*And sincerely I donĀ“t how it work, I construct my sources complete with
MIRD book data
(https://books.google.de/books/about/MIRD.html?id=zEyo06YS5NMC&redir_esc=y
<https://books.google.de/books/about/MIRD.html?id=zEyo06YS5NMC&redir_esc=y>)*

A last point if you already are fixing the activity, I am not sure but I
would expect that your calculation will give you Dose in [Gy/s], then if
you include a desintegration curve in your calculation you will get
directly Dose in [Gy].

Sorry, it was pretty long but it is how I deal with that.

Eventually you will fine an easy way, but it is the larger but with better
explanation.

Regards

2017-08-09 10:24 GMT+02:00 Niels van der Werf <nrvdwerf at gmail.com>:

> Dear all,
>
> Last week I asked a question about my simulation, which is now running
> with the help of many reactions on my previous questions.
>
> However, the results which I get from this calculation are higher than
> what I expected, with approximately a factor 2. Last week, therefore, I
> send out this question to the GATE-mailing list. Unfortunately, I got no
> response yet. I would therefore like to ask you if you maybe have the time
> to look at my question, and see if you possible have any idea where I
> should look for to acquire the correct dose results.
>
> For my simulation, I used the fluor-18 file from the dosimetry example
> from the gate-repository as my source. The simulation ran with 1 Bq in the
> brain-tissue, and 6 000 000 primary events. With a mean energy of 250 keV
> for the beta-particle of F-18 I would have expected a total deposited
> energy of 1.500.000 MeV for the 6 million primary events. However, when I
> sum over all pixel values from the resulting Edep.mhd / Edep.raw file I get
> 3.237.062 MeV.
>
> Do you have any idea where this difference comes from?
>
> Thanks in advance for your help!
>
> Kind regards,
> Niels
> _______________________________________________
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> Gate-users at lists.opengatecollaboration.org
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