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

Thu Oct 20 00:27:00 CEST 2022

Hi Nícollas,

I calculated the dose in each organ (in mGy) from Edep and then divided by the activity*time for S-Factors in mGy/MBq s.

I was just running the simulation for a fixed activity for 1 second. I used the rangeTranslator in Gate to set an ActivityRange.dat file with the Bq/voxel in each region of the image so I knew the total activity in each source region:

/gate/source/NAME/reader/insert image
/gate/source/NAME/imageReader/translator/insert range
/gate/source/NAME/imageReader/rangeTranslator/readTable ActivityRange.dat
/gate/source/NAME/imageReader/rangeTranslator/describe 1
/gate/source/NAME/imageReader/readFile source_image.h33

I assume that you could use the number of primaries for the division instead of the activity*time, but I haven't tried that function with voxelised phantoms so I am not sure how the activity gets distributed.

Best wishes,

Sophia Pells
________________________________
From: Nicollas Goncalves Cavedini <nicollas.cavedini at acad.pucrs.br>
Sent: Wednesday, October 19, 2022 22:28
To: Sophia Pells <sophia.pells at manchester.ac.uk>
Cc: gate-users at lists.opengatecollaboration.org <gate-users at lists.opengatecollaboration.org>
Subject: Re: [Gate-users] S-Values and DoseActor issues (Nicollas Goncalves Cavedini)

Hi Sophia!

Firstly, thanks for your detailed answer to my questions! About the "Ion Source", this publication by Julia Brosch is the same that I read. I was hoping that the people working in GATE development know if this bug was corrected.

About the Edep and S-Values, I was using the organ's mass and Edep for the dose calculation but how can I calculate the S-value? Should I get the division of the dose by the accumulated activity and later divide it by the number of primaries (/gate/application/setTotalNumberOfPrimaries)?

I greatly appreciate your help!

Best regards,

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.

Em qua., 19 de out. de 2022 às 11:18, Sophia Pells <sophia.pells at manchester.ac.uk<mailto:sophia.pells at manchester.ac.uk>> escreveu:
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<mailto:nicollas.cavedini at acad.pucrs.br>>
To: gate-users <Gate-users at lists.opengatecollaboration.org<mailto:Gate-users at lists.opengatecollaboration.org>>
Subject: [Gate-users] S-Values and DoseActor issues
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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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