[Gate-users] TPSPencilBeam source description

[David Boersma]

Hi Jakub,


Yes, sorry, this is a relatively new (~1 year old) addition to the "source properties" in GateSourceTPSPencilBeam.

We ("GateRTion" crowd) are even thinking about changing it yet again. 😊


If the treatment plans that you work with are specifying the spot weights in "number of ions" (option "setSpotIntensityAsNbIons" true), then in principle you do not need to worry about this, the monitor calibration will be ignored (add a dummy polynomial, maybe you can even omit it).


If it does use MU as a spot weight unit, then during commsissioning of your TPS you or your medical physicist colleagues probably had to provide tables/curves of N/MU as function of beam energy. A polynomial fit to those data would be good first try for a good N/MU calibration in the source properties file. Maybe another possibility: fit them together with the energy polynomials, if you happen to have a set of IDD curves with absolute calibration.


In older versions of Gate (8.0 and older) the N/MU calibration was hardcoded in GateSourceTPSPencilBeam. I made a polynomial fit to that calibration function and inserted it in the source properties file of the "dosimetry/dosimetry/protontherapy" example:


https://github.com/OpenGATE/GateContrib/blob/master/dosimetry/dosimetry/protontherapy/data/Source-Properties.txt


A few years ago, when I was working in Uppsala, I compared this function with the measured calibration curve of the Skandion clinic. Amazingly, they were completely compatible within the accuracy of the measurement. If the treatment machines for which you are going to perform simulations are similar to those at Skandion, then I bet that you can be optimistic about the similarity of your curve with that "standard calibration curve". 😊


About the planned change to this functionality: right now, only the shape of the N/MU curve matters, not the overall normalization factor. The spot weights (be it in N or in MU) are effectively renormalized to the number of requested primaries: if you request 10 times more primaries, then the DoseActor will record a 10 times higher dose. In order to compare with TPS dose, you need to rescale the distributions with NTPS/NMC. It has been suggested that the dose actor should apply this rescaling factor directly (this is technically not so hard, using the particle weight). This probably wouldn't affect the source properties file, but it would put stronger requirements on the quality of the fit that you provide (not only the shape, but the normalization will matter too). For the implementation, we need to take care that this will work correctly with variable number of primaries (for the SaveData functionality of the dose actor, e.g. with "everyNseconds", or in combination with the "stop on script" actor).


HTH,

David



________________________________
Von: Gate-users <gate-users-bounces at lists.opengatecollaboration.org> im Auftrag von jbaran <jbaran at ifj.edu.pl>
Gesendet: Mittwoch, 21. August 2019 13:18:44
An: Gate Users
Betreff: [Gate-users] TPSPencilBeam source description

Dear Gate Community,

According to the TPSPencilBeam source description
(http://wiki.opengatecollaboration.org/index.php/Users_Guide:Source#TPS_Pencil_Beam_source)
I have to provide 9 polynomials. I dealt with all of them. However I
have a problem to describe the beam monitor calibration in number of
particles per monitor unit (N/MU). Unfortunately, there is no
description of that in that example:
https://github.com/OpenGATE/GateContrib/blob/master/dosimetry/Radiotherapy/example5/data/Source-Properties.txt
.

Is anyone have similar problem and could provide the proper way of doing
that.

All the best,
Jakub




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