RE: [fluka-discuss]: Stopping powers for proton therapy applications

From: Francesco Cerutti <Francesco.Cerutti_at_cern.ch>
Date: Tue, 12 Aug 2014 13:30:36 +0200

Dear Luke,

> if the material 'Helium' uses liquid parameters should it be
> noted that the materials database lists it as being in the gaseous
> state?

the issue is rather subtle. Let me try to point out a few things:

The Flair database is something else wrt default FLUKA materials.
It collects the properties/definitions of plenty of material one may want
to import into his/her input file if actually appropriate.
Default FLUKA materials are the ones listed in the chapter 5 of the manual
with their main properties.
In our specific case, the two heliums you find in the Flair database are
gas at NTP (20 Celsius) and STP (0 Celsius), being the one with lower
density at NTP (and not the other way around).
The latter coincides with the default FLUKA helium (HELIUM, no MATERIAL
card needed, 0.000166 g/cm3 density), which - due to its density, three
orders of magnitude lower than the liquid one - is obviously intended by
the code as a gas.

Now, apart from the density, calculation of stopping power at low energies
implies the use of Ziegler fitting coefficients.
For helium, the only set implemented in FLUKA is the one referring to the
liquid state, which turns out to be appropriate as one defines - for
his/her current needs - liquid helium in the input.
One solution we are considering is to add also the one adopted in
ICRU/NIST, referring to gas, to be automatically applied as the current
helium is gaseous (as the default FLUKA HELIUM is).

Cheers

Francesco

**************************************************
Francesco Cerutti
CERN-EN/STI
CH-1211 Geneva 23
Switzerland
tel. ++41 22 7678962
fax ++41 22 7668854

On Tue, 12 Aug 2014, Luke Bird wrote:

> Dear Francesco and others,
>
> Thank you for looking into the issue with the stopping powers. I had considered whether the helium was in a different state but when looking at 'Helium' under the materials database accessible through flair, the physical state is said to 'gas' with a lower density of 0.00016632 g/cm^3 compared to the density of 0.0001785 g/cm^3 for the material called 'helium gas'. My thought was that the former was the density at standard temperature/pressure (STP) and the other was a normal temperature/pressure (NTP). The relative numbers seemed to agree when I looked them up from other sources. Was this coincidental and, secondly, if the material 'Helium' uses liquid parameters should it be noted that the materials database lists it as being in the gaseous state?
>
> Thanks again.
>
> Luke
>
>
> ________________________________________
> From: Francesco Cerutti [Francesco.Cerutti_at_cern.ch]
> Sent: 11 August 2014 17:57
> To: Ferreira De Almeida Lourenco, Ana
> Cc: Anna Ferrari; Luke Bird; fluka-discuss_at_fluka.org
> Subject: RE: [fluka-discuss]: Stopping powers for proton therapy applications
>
> Hi all,
>
> what is printed in the output file, when requested through DELTARAY, is
> exactly what is specified there, i.e. dE/dx in GeV/cm.
>
> All along the DELTARAY description in the manual, reference is generically
> made to "dp/dx tabulations". The actual quantity as well as the respective
> unit (!) matter when numbers are given. (Anyway, a modification of that
> manual page can still be helpful).
>
> By the way, when one looks at the latter ones, the possible confusion is
> immediately washed out: for a 10 MeV proton, dE/dx [GeV/cm] and dp/dx
> [GeV/(c cm)] differ by a factor 7 (i.e. (E+m)/p or 1/beta), not by less
> than percent.
>
> Concerning now Luke's discrepancies (few MeV alphas in gas He), they can
> be explained by the fact that the parameter set used by FLUKA for the low
> energy fitting refers to liquid helium [present in quite some amount here
> at CERN...], whereas the ICRU/NIST curve is the one of gas helium. The
> difference is related to the different state, not to the much different
> density, which is properly taken into account.
>
> Concerning Ana's fluctuation up to ~5 permil (protons in graphite), we
> need to have a deeper look into it.
>
> Kindest regards
>
> Francesco
>
> **************************************************
> Francesco Cerutti
> CERN-EN/STI
> CH-1211 Geneva 23
> Switzerland
> tel. ++41 22 7678962
> fax ++41 22 7668854
>
> On Mon, 11 Aug 2014, Ferreira De Almeida Lourenco, Ana wrote:
>
>> Dear all,
>>
>> After looking to the manual carefully, p 299, pdf manual:
>> (i) dE/dx tabulations (if requested, see DELTARAY , p. 97)
>> For each assigned material and for each charged heavy particle (hadrons, muons, recoil ions) a
>> table is printed with the following data:
>> energy, unrestricted stopping power, (= ), shell correction, restricted stopping power (ac-
>> cording to the threshold specified by the user with DELTARAY, WHAT(1) ).
>>
>> Looking at the DELTARAY description is stated that dp/dx tabulations are printed but this is not in agreement with the explanation that is stated in the manual regarding the main output (p 299)...
>>
>> Many thanks,
>> ana
>> ________________________________________
>> De: Ferreira De Almeida Lourenco, Ana
>> Enviado: 11 de agosto de 2014 13:11
>> Para: Anna Ferrari; Luke Bird
>> Cc: francesco.cerutti_at_cern.ch; fluka-discuss_at_fluka.org
>> Assunto: RE: [fluka-discuss]: Stopping powers for proton therapy applications
>>
>> Dear Anna and all,
>>
>> Many thanks for your reply.
>> I understand that FLUKA output refers to momentum loss as is stated in the manual. But I have two questions:
>> 1- Why does the momentum loss (dp/dx) is showed as energy loss (dE/dx) in the output file?
>> 2- Why do not PRINT the results as energy loss (dE/dx) since it is common and useful for medical applications?
>>
>> Many thanks,
>> Ana
>> ________________________________________
>> De: Anna Ferrari <a.ferrari_at_hzdr.de>
>> Enviado: 11 de agosto de 2014 12:55
>> Para: Ferreira De Almeida Lourenco, Ana; Luke Bird
>> Cc: francesco.cerutti_at_cern.ch; fluka-discuss_at_fluka.org
>> Assunto: Re: [fluka-discuss]: Stopping powers for proton therapy applications
>>
>> Dear Ana, dear Luke,
>>
>> Stopping powers as printed in FLUKA output refer to momentum loss (dp/dx), not
>> to energy loss (dE/dx) as reported by NIST. If you did not take into account
>> this difference you compared different quantities and this can explain the
>> "discrepancies" you see.
>> At high energies the value of proton momentum is very close to energy, so
>> FLUKA numbers seem to agree with NIST. But at lower energies, and especially
>> for particles heavier than protons, there can be no agreement. In the case of
>> Ana the discrepancy -as expected- can be observed better for graphite, which
>> has half density compared with water.
>>
>> This point was already clarified by Mario Santana:
>> http://www.fluka.org/web_archive/earchive/new-fluka-discuss/6985.html
>>
>> Hope this helps,
>> best regards,
>> Anna
>>
>>
>>
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> Anna Ferrari
>> Institute of Radiation Physics
>> Helmholtz-Zentrum Dresden-Rossendorf e.V.
>> a.ferrari_at_hzdr.de
>>
>>
>> Am Fri, 11 Jul 2014 14:05:21 +0000 schrieb "Ferreira De Almeida Lourenco, Ana"
>> <am.lourenco_at_ucl.ac.uk>:
>>> Dear FLUKA experts,
>>>
>>>
>>> I'm using FLUKA for clinical proton dosimetry applications. For validation
>>> proposes, I'm comparing the stopping powers from FLUKA with the stopping
>>> powers from ICRU.
>>>
>>>
>>> The graph below shows the ratio between FLUKA and ICRU stopping powers for
>>> water (blue) and graphite (green). As you can see I get a good agreement for
>>> water, but for graphite, specially for low energies. Could please someone
>>> explain me why do I get this disagreement for graphite? I'm using the same
>>> I-value (78eV) and density (1.7g.cm-3) that ICRU uses for graphite.
>>>
>>> [cid:8c77f38a-d52f-4644-8e83-71ffc41c5a3a]
>>>
>>>
>>> Please find attached my inp file.
>>>
>>> Many thanks,
>>>
>>> Ana
Received on Tue Aug 12 2014 - 15:01:42 CEST

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