Dear Ana
yes, the difference is in stepsizes, induced by the difference in the
delta ray production threshold. With the HADROTHERAPY default, the
threshold was w 100KeV in fluka2011.2x, it is now 300keV (The maanual is
wrong, as already pointed out by another user, and will be changed). The
reason is optimization of CPU vs precision.
The different delta ray threshold has an impact on the step size, because
steps are calculated either on fraction of energy loss, or as distance to
interaction/delta production.
The artefact you see comes from the mismatch between stepsize and binning
size: energy depositions in "long" steps will be equally distributed among
many bin, producing a staircase distribution.
Note that the transport is more precise than scoring: energy loss is
correcly integrated along the step.
Solutions: either increase the bin size, or include a DELTARAY card with
threshold at 100keV in water
Apologies for the lack of documentation on the changes
Paola
> Dear FLUKA experts,
>
> I'm simulating proton beams (beamlets) of various clinical energies
> (50-250 MeV) in water and scoring dose in function of depth. I've run
> these simulations with the FLUKA 2020 Version 0.3 and compared with
> previous results from FLUKA 2011 Version 2x.4 (same input file). Below the
> ratio of dose in function of depth obtained with FLUKA 2020 and FLUKA 2011
> for three energies (figure 1).
>
> The artefacts at shallow depths (figure 2 and 3) seem to be related with
> particle step sizes or energy production thresholds. Looking at the output
> files, different particle thresholds are being used although the input
> cards are the same.
>
> I'm not sure what I may be doing wrong. What have changed between versions
> that could explain these results?
>
> Example of input and output files attached.
>
> Many thanks and best wishes,
> Ana
>
> Figure 1 - Ratio of dose in function of depth
> [cid:57feb0e6-aca2-4c7a-8a5f-6a4e96913ea0]
>
> Figure 2 - Depth-dose curves
> [cid:c2d4ad39-a36c-4dc8-916c-13cd8df34f01]
>
> Figure 3 - Zoom at shallow depths of depth-dose curves
> [cid:c9acf02a-9c9c-4f6f-bf10-8c0431ddd375]
>
Paola Sala
INFN Milano
tel. Milano +39-0250317374
tel. CERN +41-227679148
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Received on Sat Sep 05 2020 - 18:32:02 CEST