RESNUCLEI scoring returns zero for voxel geometry (carbon ion beam simulation)

Scoring
1

Dear experts,

I am a beginner in FLUKA and currently learning how to simulate positron-emitting nuclides generated by carbon ion beams in human tissues.

I have converted a CT dataset into a voxel geometry and set up several detectors to score dose, activity, and nuclide production. For residual nuclei production, I used two approaches:

  1. USRBIN with RES-NUCL + AUXSCORE, which I understand can provide the spatial (3D) distribution of a selected nuclide;

  2. RESNUCLEI, which I understand should provide the full list of produced residual nuclei and their total yields within a given region.

As a validation step, I first performed simulations using a simple PMMA phantom. In that case, both methods worked as expected and produced reasonable results.

However, when I replaced the PMMA phantom with the CT-based voxel geometry, the RESNUCLEI results are all zero.

I would like to ask:

  1. Is my understanding of USRBIN (RES-NUCL + AUXSCORE) and RESNUCLEI correct?

  2. Why does RESNUCLEI return zero results when applied to voxel geometry, while it works for a simple PMMA phantom?

  3. Is there any specific requirement or limitation when using RESNUCLEI with voxel geometries?

For reference, I have attached:

  • The input (.inp) file

  • The voxel geometry files

  • The RESNUCLEI output file

I would greatly appreciate any guidance or suggestions.

Thank you very much for your help!

Best regards,

Input files

Please upload all relevant files. (FLUKA input file, Flair project file, user routines, and data files)

lung_23_tab.lis (669 Bytes)

lung_23_sum.lis (934 Bytes)

lung.inp (2.2 KB)

voxel.vxl (5.9 MB)

4

Dear @yang_xy,

  1. Is my understanding of USRBIN (RES-NUCL + AUXSCORE) and RESNUCLEI correct?

Yes, you understand them correctly

  1. Why does RESNUCLEI return zero results when applied to voxel geometry, while it works for a simple PMMA phantom?

Please check the input which you shared; all voxel regions have a Vacuum material assigned to them. Additionally, WHAT(5) in RESNUCLEi must be set to -1 or @ALLREGS to consider every region, right now it’s set to voxels’ cage region which is filled with Vacuum.

  1. Is there any specific requirement or limitation when using RESNUCLEI with voxel geometries?

Voxels might have a special description of material in terms of HU values and might use CORRFACT card, modifying their density so that when you are scoring mass-specific quantity, these factors must be considered in normalisation.

You can go through our Medical applications lecture for more details.

Best regards,
Volodymyr

5

Thank you very much for your detailed explanation, and apologies for the late reply.
I now fully understand the issue. Your clarification was very helpful.

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