Re: Clarification of DOSE-EQ units in a USRBIN estimator

From: Anna Ferrari <a.ferrari_at_hzdr.de>
Date: Sun, 15 Apr 2012 23:48:37 +0200

Dear Mina,

no, the problem must not be seen in this way.
The units are exactly as written in the manual and as you reported:

13) The results from USRBIN are normalised per unit volume and per unit
primary weight,except for (...) and for dose equivalent,
        <==============
expressed as pSv per unit primary weight. <==============

First: it does not make sense to express the dose equivalent in pSv/cm3!
You have always to remember how an average dose equivalent in a given volume
is evaluated: you calculate the average fluence (in part./cm^2 per primary) of
the components of the radiation field in the volume and then you apply the
appropriate conversion coefficients (in pSv cm^2) to get the dose equivalent
due to this average radiation field . To each point of the volume you
associate then this average dose equivalent, which is expressed in pSv/primary
(thinking to the meaning of the dose equivalent is helpful).

Let's think then about your examples:

a) USRBIN scoring with space binning
An average radiation field is calculated in each element of the defined USRBIN
mesh in the space. The dose equivalent values you get (in pSv/primary) refer
to these elements. They refer to 1 cm^3 volumes only if you have set this
granularity.

b) USRBIN scoring with region binning
We have to take care here.
The manual states that this is the only case where USRBIN results are NOT
normalized by volume. The delicate point is that at the moment this is not
dependent on the specification or not of the volume in the geometry section,
which applies only to the quantities calculated via the SCORE option.
[ From the FLUKA manual, section: 2.2.6:
"The only effect of specifying region volumes is to normalise per cm3 the
quantities calculated via the SCORE option (...): for other estimators
requiring volume normalisation the volume is input as part of the detector
definition (USRTRACK, USRCOLL, USRYIELD), or is calculated directly by the
program (USRBIN)", where the last sentence refers only to the USRBIN scoring
with space mesh (I admit here it is not too clear).]

This means that with the region binning option you will not get the average
fluence in the volume (in part/cm^2), but the total tracklength in the
selected region. To get the fluence and finally the correct average dose
equivalent (always in pSv/primary) you have to divide offline by the volume.
I think this is a complication (!) that can be easily avoided by using USRBIN
with space mesh, a choice that I prefer also under the dosimetric point of
view (I can choose how well I want to approximate the radiation field -and
then the dose equivalent calculation- and I can avoid to average on large
volumes, with probable dangerous underestimations of the dose in critical
points).

Last: yes, you know already that with the IRRPROF card you pass from pSv/prim
to pSv/s, because you input the current in prim/s.

I hope this helps to clarify a bit,
best regards,
Anna

Am Thu, 12 Apr 2012 13:05:43 -0700 schrieb Mina Nozar <nozarm_at_triumf.ca>:
> Dear FLUKA users, can someone confirm whether the following statements are
>correct?
>
> - USRBIN scoring (spacial binning)
> pSv/cm^3*prim - with no IRRPROF card
> pSv/cm^3*sec - with an IRRPROF card
>
>
> - USRBIN scoring (region binning)
> pSv/prim - with no IRRPROF card and with no volume input for the given in
>the geometry section)
> pSv/sec - with an IRRPROF card and with no volume input for the given in
>the geometry section)
>
>
> pSv/prim - with no IRRPROF card and with the region volume given in the
>geometry section)
> pSv/sec - with an IRRPROF card and with the region volume given in the
>geometry section)
>
>
> So regardless of whether region volumes are given in the geometry section,
>units are pSv/prim or pSv/sec in the region
> binning? This is how I interpret the manual under USRBIN:
>
>
> 13) The results from USRBIN are normalised per unit volume and per unit
> primary weight, except for region binnings and special user-defined
> binnings, which are normalised per unit primary weight only, for
> DPA, which are given as number of displacements per atom per unit
> primary weight, averaged over the bin volume, and for dose
> <==============
> equivalent, expressed as pSv per unit primary weight.
> <==============
> In case symmetries are requested, proper rescaled volumes are taken
> into account for normalisation (that is, an extra factor 2 is
> applied to the volume if symmetry around one plane is required, 8 if
> the symmetry is around the origin)
>
>
> Thank you for the clarification,
> Mina
>
Received on Mon Apr 16 2012 - 09:30:39 CEST

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