Dear Francesco,
Thank you very much for your clarification and sharing of your knowledge.
Yes, I forgot to mention that I have divided usrbin region energy scoring by volume and by density to get a dose(kerma). All that explanation about dose and energy scoring your wrote in the past discussion topics was essential for understanding all these concepts for the successful simulations with Fluka.
I have missed this point from your first mail: "photon track-length [cm], namely the path travelled by photons over that region. If you divide this quantity by the region volume, you get the *average* photon fluence [cm-2] over that region." -->> now, when I got it finally, everything makes sense - thank you very much once more.
Regarding integration - " provided that the region coincides with the integral volume " - I made mistake here because the integration was done over whole Cartesian, and not a region. Now the integration gives the same result, as it should be. Thanks again,
Best Regards
Alexander
-----Original Message-----
From: Francesco Cerutti <Francesco.Cerutti_at_cern.ch>
Sent: Wednesday, 30 January, 2019 15:29
To: Ševčik Aleksandras <aleksandras.sevcik_at_ktu.edu>
Cc: fluka-discuss_at_fluka.org
Subject: RE: [fluka-discuss]: RE: spectrum normalization and actual dose
Dear Alex,
deposited energy [MeV] and tracklength [cm] scale with the volume (the larger the volume, the larger their value), while dose [Gy], energy density [GeV/cm3] and fluence [cm-2] don't, since they are the above ones divided by the respective volume.
Now, technically:
USRTRACK divides by the respective region volume only if you put the latter in the USRTRACK card. Otherwise, you can easily divide yourself as you handle the results. Assuming that this division is made (by the code or by yourself), if you eventually integrate over energy (something that actually you do not really need to do, since you find it already done in the _sum.lis file), you will indeed get GeV/cm^2 for ENERGY scoring (that is a rather weird scoring choice for USRTRACK, since in that case it's not deposited energy, rather particle kinetic energy). But you will get photon/[cm^2] for PHOTON scoring, and not photon/[cm^2*MeV], since you integrated over energy (DX*).
As for USRBIN region ENERGY scoring, if you divide by the region material
(air) density, you do not get dose [GeV/g], you get something [GeV*cm3/g] that needs to be further divided by the region volume to become (the
average) dose.
Finally, the 3D integral (DX*DY*DZ*) of the fluence scored by USRBIN Cartesian PHOTON gives definitely the same photon tracklength as obtained by USRBIN Region PHOTON, provided that the region coincides with the integral volume. If instead you plot in Flair the photon fluence as a 1D distribution (e.g. in X) and you multiply by DX only, you are producing a quantity of less evident meaning.
I think I answered at the beginning your first question. The ICRP units refer to dose and fluence, which do not scale with the reference volume.
About "per primary", it does not refer to tracklength, but to the 'beam'
particle. This way, one can scale results with the actual source (beam) intensity (i.e. physical number of primary particles).
I have no idea how you integrated the photon fluence spatial distribution.
As indicated above, a proper 3D integration must give back the tracklength in the region, as it does.
Cheers
Francesco
**************************************************
Francesco Cerutti
CERN-EN/STI
CH-1211 Geneva 23
Switzerland
tel. +41 22 7678962
On Wed, 30 Jan 2019, Ševčik Aleksandras wrote:
> Thank you very much Francesco,
>
> Yes, now everything is starting to make sense. I know that all this is written in the manuals, however, until one starts to make the actual simulations, it sometimes hard to grasp some concepts at once. Just to be totally sure, I run kerma simulation for 1x1x1 rpp air body body with 1 MeV and emfcut. The value I got is equal to air kerma free-in-air value in ICRP119 so I suppose it’s ok. Now scoring:
> USTRACK ENERGY integrated fluence DX*Y and normalizing for MeV - the
> result is ok , y= 1 MeV/cm^2 per primary USTRACK PHOTON integrated fluence DX*Y , the result is ok , y=1 photon / [cm^2*MeV] per primary (hope I got the units correctly).
> USRBIN Region Photon - I got 1, so photon track length 1 cm USRBIN
> Region Energy - value in GeV for total region volume, dividing by air density gives GeV/g (dose(kerma)) equal to ICRP119 value.
> USRBIN X-Y-Z Energy - spatial distribution GeV/cm^3 per primary, integrating over it gives the same as USRBIN Region Energy.
> USRBIN X-Y-Z Photon - spatial distribution of photon fluence
> photons/cm^2 per primary. Integrating over it gives ~11 (?)
>
> Could you please:
> 1) When I run the same simulation with different volumes, I can see
> that kerma value is directly proportional to photon track length, but
> not to *average* photon fluence [cm-2] over the region. For example
> rpp 2x2x2 gives tracklength 2 cm, 4x4x10 gives tracklength 10 cm,
> while average photon fluences would be 2/8 and 10/160 accordingly. But
> the kerma value is exactly 10 times higher with larger volume. Why
> then ICRP gives this value in pGy*cm^2 ? Just trying to understand the
> rationale behind the measurement units,
> 2) In measurement units, when we state "per primary", what does it actually, in layman terms, means? Does it relates to tracklength as well?
> 3) Why integrating USRBIN X-Y-Z Photon I got 11 ?
>
> I will greatly appreciate your help as in my educational environment I work only with experimental guys who don't have a clue about actual mc modelling.
>
> Regards
> Alex
>
> -----Original Message-----
> From: Francesco Cerutti <Francesco.Cerutti_at_cern.ch>
> Sent: Wednesday, 30 January, 2019 10:36
> To: Ševčik Aleksandras <aleksandras.sevcik_at_ktu.edu>
> Cc: fluka-discuss_at_fluka.org
> Subject: Re: [fluka-discuss]: RE: spectrum normalization and actual
> dose
>
>
> Hi Alex,
>
> you do not get the photon number, you get a more meaningful quantity that is the photon tracklength [cm], namely the path travelled by photons over that region. If you divide this quantity by the region volume, you get the *average* photon fluence [cm-2] over that region. Other kinds of USRBIN (Cartesian and cylindrical) give you directly photon fluence, since they already divide by the respective regular bin volume. If in turn you multiply that by the latter, then you get again photon tracklength. All physical effects (energy deposition, i.e. dose, and detector response) depend on the particle tracklength, not the particle number.
>
> Kind regards
>
> Francesco
>
> **************************************************
> Francesco Cerutti
> CERN-EN/STI
> CH-1211 Geneva 23
> Switzerland
> tel. +41 22 7678962
>
> On Wed, 30 Jan 2019, Ševčik Aleksandras wrote:
>
>>
>> Dear all,
>>
>> It seems that my question most likely unclear, so let me rephrase it
>> to be more specific and technical:
>>
>>
>>
>> When scoring PHOTONS using usrbin region, do you get the total or
>> average photon number in the region for that specific simulation?
>> Then total number of photons in the region can be get by integrating
>> usrbin photon x-y-z scoring?
>>
>>
>>
>> A.
>>
>>
>>
>> From: owner-fluka-discuss_at_mi.infn.it <owner-fluka-discuss_at_mi.infn.it>
>> On Behalf Of Ševcik Aleksandras
>> Sent: Friday, 25 January, 2019 01:13
>> To: fluka-discuss_at_fluka.org
>> Subject: [fluka-discuss]: spectrum normalization and actual dose
>>
>>
>>
>> Dear experts,
>>
>>
>>
>> I would like to get the actual dose values from the simulation and
>> want to know if the approach below is valid.
>>
>> I am using source.f to generate realistic x-ray beam from specialized
>> x-ray simulation software which gives me the spectrum and fluence.
>> Integrating it I can get the estimated actual number of photon, let’s
>> say 10E7. In the simulation I can use USRBIN for all regions to score
>> the overall number of photons detected in the simulation, let’s say
>> 10E2. So in the same simulation I can use this factor 10E7/10E2 for
>> dose values as well to get the actual dose values for the specific x-ray tube.
>>
>> I have tried to run the test simulation with 100x100x100 water cube
>> in the vacuum. In the beginning I was integrating usrtrack fluence
>> energy spectrum but later saw that usrbin region photon scoring gives
>> the same value. So multiplying usrbin total dose value by this
>> fluence actual/simulated factor and converting it to Gy gives me
>> around 7E5 Gy – as it was expected from 80 kvp *1 mAs_at_1meter x-ray beam.
>>
>> However if this approach is not valid, I would appreciate any comment
>> what would be the correct way to do this.
>>
>>
>>
>> Regards
>>
>> Alexander
>>
>>
>>
>
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Received on Thu Jan 31 2019 - 01:28:16 CET