[Gate-users] Questions about LET and average LET calculation in Gate

Andreas Resch andreas.resch at meduniwien.ac.at
Tue Mar 29 11:09:03 CEST 2022

Dear Guangru Li,

thank you for carefully reading the Gate documentation. Indeed, the user 
manual was not consistent and up to date. I just changed it (you can 
look at it in the pull request now, or in the official documentation in 
some days).

1. It is computeElectronicDEDX ; note that the restricted LET 
calculation option, which the second sentence referred to, is now 
removed in the documentation as this implementation is not sufficiently 

2. Parallel computation: If you only simulate on a single CPU you do not 
need to worry about it. However, if you split your simulation into 
several simulations I would recommend the following. Looking at the 
formula for e.g. dose averaged LET:

  let's assume this is the sum over all contributions and Ld = n/d. Now 
this shall now be randomly subdivided into j computations, the numerator 
would look like n = n1 + n2 + ... nj and d correspondingly. Ld = (n1 + 
n2 + ... ) / (d1 + d2 + ...);  Therefore, the LET actor allows you to 
score the numerator and denominator of this equation separately.



Am 2022-03-29 02:34, schrieb 李广儒:

> Dear Gate users,
> I'm trying to calculate LET and average LET(including dose-average and 
> track-average) by Gate. But I met some problems.
> First, I found that in the user guide, it says that
> "_DoseAveraged (default) or TrackAveraged LET both calculated by using 
> the Geant4 EMCalculator method -GetElectronicStoppingPowerDEDX_". But I 
> checked the manual of Geant4(Application Developers Guide) and found 
> that there is a "_ComputeElectronicDEDX method_" in G4EmCalculator 
> class as shown below:
> So I think maybe it use _ComputeElectronicDEDX method_ ,not 
> _GetElectronicStoppingPowerDEDX_. It maybe a little mistake in the 
> manual of Gate in my opinion.
> Second, if Gate use _ComputeElectronicDEDX method,_ the LET  is 
> calculated by kinetic energy of particles as  below:
> "_Instead of computing the LET as the quotient between the actual 
> electronic energy loss and step length_
> _computed during the simulation, we calculated the LET of the step, 
> Lsn, as the corresponding_
> _mean energy loss per unit path length in the material according to the 
> proton kinetic energy_
> _at the step. In our code, Lsn was obtained with the method 
> ComputeElectronicDEDX() of_
> _G4EmCalculator class."_
> These are indicated in the _Cortés-Giraldo M A and Carabe A 2015 Phys. 
> Med. Biol. 60 2645-69_.But I wonder what method was used to calculate 
> DoseAveraged and TrackAveraged LET in Gate_._
> And it's very confusing to me. Because it also said in the Gate manual 
> that if I use parallel computation, there will be _"2 output images for 
> each LET actor and run, a file labeled as '-numerator' and one labeled 
> as '-denominator'. Building the quotient of these two images results in 
> the averaged LET image. Note that the numerator and denominator images 
> have to be summed up before the division."_So why there are 2 outputs? 
> And what are physical meanings of  _denominator and  numerator ?_
> Best,
> Guangru Li
> _______________________________________________
> Gate-users mailing list
> Gate-users at lists.opengatecollaboration.org
> http://lists.opengatecollaboration.org/mailman/listinfo/gate-users
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