Re: [fluka-discuss]: Secondary protons from a scattering clinical proton beam in water and graphite phantoms

From: Francesco Cerutti <Francesco.Cerutti_at_cern.ch>
Date: Sun, 25 Oct 2015 16:13:46 +0100

Dear Ana,

I think you missed the point. The secondary proton difference you observe
with water is not due to scattered beam particles (nor to proton
production in non-elastic reactions), rather to recoiling H nuclei (from
nuclear elastic events), which are protons as well and in graphite do not
exist. Of course you get them also with a mono-energetic beam.

Kind regards

Francesco

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

On Sun, 25 Oct 2015, Ferreira De Almeida Lourenco, Ana wrote:

> Dear Francesco and all,
>
> Thank you for your e-mail. I'm aware of the difference in scatter between the materials. For a mono-energetic beam differences in fluence (at equivalent depths) have been reported to be of the order of 1% at the surface which is mainly attributed to the contribution of alpha particles. This is well understood due to the production cross sections of these particles per atomic mass.
>
> However, what I'm getting with these results (when simulating the configuration beam line) is a difference of 20% at the surface at equivalent depths for secondary protons. If this is mainly due to scatter, then you should see this effect for a mono-energetic beam as well and this is not verified.
>
> Many thanks,
> Ana
>
> ________________________________________
> De: Francesco Cerutti <Francesco.Cerutti_at_cern.ch>
> Enviado: 23 de outubro de 2015 21:43
> Para: Ferreira De Almeida Lourenco, Ana
> Cc: fluka-discuss_at_fluka.org
> Assunto: Re: [fluka-discuss]: Secondary protons from a scattering clinical proton beam in water and graphite phantoms
>
> Dear Ana,
>
> the explanation for your findings looks pretty obvious, logical and
> physical: water (H2O) happens to contain 'free' protons as H nuclei (with
> 'free' I mean not bound to other nucleons inside a heavier nucleus, like
> C and O), so the secondary protons you see in that case are the ones put
> in motion - without the need for being 'produced' - by nuclear elastic
> scattering on H.
>
> Cheers
>
> Francesco
>
> **************************************************
> Francesco Cerutti
> CERN-EN/STI
> CH-1211 Geneva 23
> Switzerland
> tel. ++41 22 7678962
> fax ++41 22 7668854
>
> On Fri, 23 Oct 2015, Ferreira De Almeida Lourenco, Ana wrote:
>
>>
>> Dear Fluka experts,
>>
>>
>> I have simulated in FLUKA a clinical 62 MeV proton scattering beam and I'm studying the
>> dose due to secondary protons in a phantom of water and graphite.
>>
>> I'm using a USRBIN card to score dose due to primary protons (by scoring BEAMPART) and
>> protons (by scoring PROTON). Please find attached the results of the USRBIN card for
>> primaries and protons in the water and graphite phantom, where the phantom is at
>> position z=184 cm.
>>
>>
>> The results show that the contribution from PROTON is significantly different in water
>> and graphite. Also, considering that PROTON-BEAMPART = secondary protons, we conclude
>> that these difference comes from secondary protons (since the difference from BEAMPART
>> is very small).
>>
>>
>> Looking at the production cross section for secondary protons from ICRU 63 (graph in
>> attachment) it is unrealistic to obtain such a big difference between water and graphite
>> for secondary protons. I can't find a logical interpretation that explain these results,
>> unless that the cross sections implemented in FLUKA are considerable different from
>> those in ICRU 63.
>>
>>
>> Why the contribution of sec protons is so different in water and graphite? Could you
>> please provide info regarding the nuclear data that is implemented in FLUKA?
>>
>>
>> I have also attached the input files for water and graphite.
>>
>>
>> Many thanks,
>>
>> Ana
>>
>>
>>
>

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Received on Sun Oct 25 2015 - 17:48:28 CET

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