[Gate-users] S-Values and DoseActor issues (Nicollas Goncalves Cavedini)

[Sophia Pells]

Hi Nícollas,

I've calculated S-factors for Lu-177 in Gatev8.2 before so I will have a go at answering your questions:

1) Is the "Ion Source" recommended for this?
There have been reported issues with the ion source for Lu-177 in some versions of Geant4, particularly v10.5.0 (see http://lists.opengatecollaboration.org/pipermail/gate-users/2019-November/011175.html). It may have been fixed in later versions but I would still recommend using a UserSpectrum and defining the source yourself so you know exactly what photon, beta, mono-energetic electron data is being used (the mono-energetic electron emission energies and intensities especially vary quite a bit with different data sources).

2) ) Is the "DoseActor" the best way to record the dose?
I used the DoseActor, but found the Edep output was more useful than the Dose output (for my applications) . This gives the energy deposited in each voxel (in MeV). It can be enabled with the commands:

/gate/actor/NAME/enableEdep             true
/gate/actor/NAME/enableUncertaintyEdep  true

Note that the uncertainty is relative.

3) How do I calculate the S-values?
The Edep output gives the energy deposited in each voxel of the image. I would use a set of VOIs and ImageJ to get the total energy deposited in each organ (sum over the slices) and use that with the organ mass to calculate the dose and S-factors.  I had to run each source organ as a separate simulation due to memory limitations and then sum the contribution from each source region for each target region. I would recommend avoiding the particleFilter actor as I got some weird results with this (they might have been fixed since I used it). I would just run separate simulations to get the separate contribution from photons, betas etc.

OpenDose is a great resource for S-factors. I validated my simulations by downloading the ICRP 110 AF phantom and comparing my S-factors with the ones on OpenDose.
https://www.opendose.org/svalues

Hope this helps!

Best wishes,

Sophia

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Today's Topics:

   1. S-Values and DoseActor issues (Nicollas Goncalves Cavedini)


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Message: 1
Date: Tue, 18 Oct 2022 08:31:29 -0300
From: Nicollas Goncalves Cavedini <nicollas.cavedini at acad.pucrs.br>
To: gate-users <Gate-users at lists.opengatecollaboration.org>
Subject: [Gate-users] S-Values and DoseActor issues
Message-ID:
        <CAMTcvva3g8_War69zqXf=JTT7CBUo77VTXsmWgitpz7Nywfv+A at mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

Dear GATE Users, I am sending this email again as I have not received a
response.

I am working on my PhD project with PET/CT images of prostate cancer and I
have some questions about anthropomorphic phantom simulations. I intend to
perform simulations with 177Lu using the "Golem" phantom from GSF Family.

My questions are:
1) Is the "Ion Source" recommended for this?

2) Is the "DoseActor" the best way to record the dose? I was searching in
the previous e-mails and I have found a report that the DoseActor may not
be the most suitable resource for this application.

3) How do I calculate the S-values? For each simulation, I get the absorbed
dose in each organ, but how do I "transform" this into S-values? We have
PET images with 4 time points after the injection and I can extract the
accumulated activity (Ã).

Any help is appreciated!

*Atenciosamente,*

*Nícollas Gonçalves Cavedini*
BSc in Physics - PUCRS
M. Eng. in Electrical Engineering - PUCRS
PhD student in Biomedical Gerontology - PUCRS

Medical Image Computing Laboratory (MEDICOM)
Contact: +55 (51) 99922-9957
Porto Alegre, Brazil.
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