# Re: [fluka-discuss]: Voxel geometry - region dose scoring - it it valid?

From: Francesco Cerutti <Francesco.Cerutti_at_cern.ch>
Date: Sat, 11 Mar 2017 15:15:00 +0100

Dear Alex,

with dose to the tumour it's indeed meant the average dose over the tumour
mass. However, in this case one usually has a pretty uniform distribution,
meaning that the dose value remains rather constant over the tumour mass.

Now, the alternative procedure you mention (scoring ENERGY per region and
then dividing by the region mass) is totally equivalent to the one you
adopted (scoring DOSE per region - which turns out to be ENERGY divided by
the region material density, i.e. GeV/(g/cm3) that as already explained
for the special case of score per region is not a dose, but the product
dose*volume - and then dividing by the region volume). In both cases you
will get the average dose over the region (the total dose does not exist).

Best

Francesco

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

On Sat, 11 Mar 2017, Ševčik Aleksandras wrote:

>
> Dear Francesco,
>
> Thank you very much for the explicit explanations. I chose wrong keywords so couldn't find the
> previous discussions in the forum. So to normalize usrbin*region DOSE, I need to multiply it by
> GeV/g-Gy conversion value and divide my voxel region volume in cm3.
>
>
> And then I'll get the *average* dose over the region. It took me some time to grasp the idea as I
> can't recall such concepts in my field/studies. Do I understand correctly that if I want to have
> the total absorbed dose ( the quantity medical physicists are using, I suppose) then I actually
> need to score the usrbin*region ENERGY which is the total energy deposition over the region (GeV )
> then normalize to it to J and finally divide  by mass of the region to get the total absorbed dose.
>
>
> I'm actually little bit confused now... what actual quantity the medical physicists have in mind
> when saying for example "the tumor should get 50 Gy in 5 days". Do they mean *average* dose over
> tumor or the total energy deposited within the tumor volume?
>
>
> Regards,
> Alex
>
> ___________________________________________________________________________________________________
> From: Francesco Cerutti <Francesco.Cerutti_at_cern.ch>
> Sent: Saturday, March 11, 2017 12:53:40 PM
> To: Ševčik Aleksandras
> Cc: Alfredo Ferrari
> Subject: Re: [fluka-discuss]: Voxel geometry - region dose scoring - it it valid?
>
> Dear Alex,
>
> there are two basic flaws in your approach, already discussed in this
> forum, e.g. here:
> http://www.fluka.org/web_archive/earchive/new-fluka-discuss/6342.html
>
> First, you talk about "integral" dose and "total" absorbed dose of the
> specific region, suggesting that you aim for a sum over the region. But
> dose is not an extensive quantity, as instead deposited energy is,
> therefore its value on a region represents the *average* over the region,
> which - in case of not uniform distribution - is lower than local dose
> values inside the same region.
>
> Second, you forget that USRBIN *per region* (contrary to Cartesian or
> cylindrical USRBIN) cannot normalize by the (region) volume, so the
> quantity that you find is GeV/(g/cm3), i.e. GeV*cm3/g and not GeV/g. This
> implies the need for dividing a posteriori by your region volume (in
> addition to the GeV -> mJ conversion). This way you will get the *average*
> dose over the region.
>
> Cheers
>
> Francesco
>
> **************************************************
> Francesco Cerutti
> CERN-EN/STI
> CH-1211 Geneva 23
> Switzerland
> tel. ++41 22 7678962
> fax  ++41 22 7668854
>
> On Sat, 11 Mar 2017, Ševčik Aleksandras wrote:
>
> >
> > Dear experts,
> >
> >
> > Currently I'm simulating an isotope dose distribution in the anthropomorphic human head phantom
> (25
> > regions representing different tissues). For the overall picture USRBIN Dose tally goes well, but
> I
> > also need the integral dose over the specific voxel regions(organs), i.e. to know total absorbed
> > dose of the specific region.
> >
> >
> > For that purpose I used USRBIN Region point parameter and selected the particular region. The
> > result I got is attached, i.e. simply the number which supposedly  should be normalized
> (multiplied
> > by 1.602176462E-7) to get it in Gy.
> >
> >
> > My question if this approach is correct as I have some doubts that I am oversimplifying it
> >
> >
> > Many thanks for any comments/input,
> >
> >
> > Rgds
> >
> > Alex
> >
> >
> >
>
>

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Received on Sat Mar 11 2017 - 16:16:35 CET

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