RE: max number of voxels

From: Valery Taranenko (
Date: Thu Apr 05 2007 - 16:44:09 CEST

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    Dear Paola,

    Thank you for the exhaustive explanation.

    In our research group we have recently finished construction of a series of
    phantoms representing a pregnant female at different period of gestation.
    The organs are represented by 3D polygonal meshes and we can voxelize them
    virtually at any resolution. The thing is, 1-mm voxels are quite common
    today, and although we can voxelize at lower resolution (thanks to the
    original organ meshes) we would like to stick with 1-mm for direct
    comparison with Penelope and EGSnrc codes. Standard MCNP/X can't deal with
    more than about 25 million voxels, but we are working on it.

    Can you set dynamic memory allocation for voxel input? This could be a best
    solution (although I'm not sure how this fits in your development habits).
    Strategically I would expect an increase in demand from people to run voxel
    phantoms with higher resolution. And here dynamic memory allocation would
    keep (presumably) low overhead for smaller phantoms but also will allow to
    go to higher voxel numbers.

    You know, today 2 GB of random-access memory is really common. Therefore
    physical memory limit (RAM) shouldn't be a problem. Presently we have 36
    organs (unique voxel IDs) and 20 unique materials, a couple of them could be
    with different densities. Ultimately we may need to go to 100 organs (this
    is very typical nowadays in this business of whole-body phantoms). I assume
    a limit on materials number is independent from voxel input (it should be).

    Scoring. The program minimum is to calculate average organ absorbed dose in
    each organ; that is, calculate absorbed energy in all voxels (mass
    normalization can be obviously done outside of Fluka without problem). Kerma
    calculation would be of an interest as well. The program maximum (for
    radiotherapy) is: calculate special distribution of dose in each voxel
    (average over a voxel). Although I found very clear explanation on how to
    input a voxel phantom, I didn't really found anything on how to score within
    it (when searched for "voxel" in manual PDF, all results relate to geometry
    input). I know I need to read the whole manual... but If you comment on how
    to score (at least simple average organ dose) this would be very helpful.

    Multi-group low energy neutrons. As far as I know people hesitate to use
    Fluka at low energies(?) in dosimetry applications for neutrons (only?) due
    to multi-group approach at energies below 20(?) MeV. My task is very
    simple--I need to calculate dose conversion coefficients (basically absorbed
    dose with appropriate normalization for source fluence) for external
    neutrons from thermal energies up to 100 GeV. Obviously following
    secondaries is important. Typically people split the energy range in two
    parts: table-based region--below 20 or 150 maybe MeV (like in MCNP/X); and
    the rest. Tell me, is it too bad to use Fluka at low neutron energies? What
    about protons (100 MeV--100 GeV)?

    I'm aware of the extensive work done by Maurizio Pelliccioni in radiation
    protection. Dr. Pelliccioni is like an apostle of all Fluka calculations for
    phantom, with many papers which I'm going to look at meanwhile.

    As a quick solution, can you recompile the code with 400 million voxel array

    Please excuse the large number of my questions. I've just embarked on the
    Fluka and expect to have a great time with it!

    Thank you,

    Valery Taranenko, Ph.D.
    Postdoc Research Associate, RPI,
    Troy, NY

    -----Original Message-----
    [] On Behalf Of paola sala
    Sent: Thursday, April 05, 2007 4:19 AM
    To: Valery Taranenko
    Subject: Re: max number of voxels


    there is no fixed limit for the number of voxels, BUT
    there is a limit given by memory:
    FLUKA stores all initialization and scoring data in an
    indexed blank common. At present this common is set to a
    dimension of 200MB. Since each voxel needs an integer*2 storage,

    if all the memory could be used for the voxels ( that is never true) the
    max n. of voxels would be 100 million.

    In practice, the max. number will depend on the problem : n. of
    materials, binning structures etc. The program stops with an error
    message if the memory limit is exceeded.

    In case you really need 400 million voxels, the program should be
    re-compiled with a much larger memory limit. This could bring to a
    severe loss of computing efficiency if the computer does not have enough
    physical memory... let me know

    On Wed, 2007-04-04 at 18:01 -0400, Valery Taranenko wrote:
    > Hi,
    > I would like to input 400 million voxel phantom into Fluka (these are
    > 1-mm voxels).
    > I could not find in the manual any limitations associated with the
    > maximum voxel number.
    > The number of organs is below 100.
    > Thank you.
    > Regards,
    > Valery Taranenko, Ph.D.
    > Postdoc Research Associate, RPI,
    > Troy, NY

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