Questions in positron-emitter yield fractions from RESNUCLEi

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1

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FLUKA:4-5.1
Flair:3.4-5

Description

Dear FLUKA experts,

I would like to ask for your help regarding the calculation of positron-emitting isotope yields using RESNUCLEi, and a discrepancy I observe when comparing my results with published literature obtained using GATE.

My goal is to obtain the relative yields of positron-emitting nuclei produced by a 12C ion beam irradiating a PMMA target.

Using RESNUCLEi scored in the entire PMMA target region, I extract the isotope yields from the Residual nuclei distribution (A\Z table) and normalize each positron emitter to the sum of all β⁺ emitters. My results are:

Nucl Yield Percent (β+)

11C 5.94e-02 80.05 %

15O 6.32e-03 8.52 %
10C 3.24e-03 4.37 %
8B 2.55e-03 3.44 %
13N 1.35e-03 1.82 %
12N 5.04e-04 0.68 %
9C 4.05e-04 0.55 %
17F 2.69e-04 0.36 %
14O 1.70e-04 0.23 %

However, published results obtained with GATE (see attached figure) show that the yield fraction of 8B is very small.
From a physical point of view, 8B is not expected to contribute such a large fraction, therefore I believe my result is likely incorrect, but I am not able to identify the source of the discrepancy.

I have attached my FLUKA input file for reference. I would greatly appreciate your help in understanding:

  • whether my procedure for extracting positron-emitter yields from RESNUCLEi is correct, and

  • what could cause the discrepancy of nuclide yield, such as 8B and 14O compared to GATE and literature results as followed:
Positron emitter Half-life Yield (%) Fraction of total yield (%)
11C 20 min 13.437 71.14
10C 19 s 1.681 8.9
15O 173.6 s 2.375 12.57
14O 91 s 0.359 1.9
13N 10 min 0.806 4.27
12N 11 ms 0.213 1.13
8B 770 ms 0.017 0.09
Thank you very much for your time and help.

Best regards,
Yang

A002.inp (4.3 KB)

Input files

3

Hi @yang_xy

Thank you for your question! Sorry for the late answer, i was on vacations.

I will have a look into your problem in the coming week.

Cheers,

Jerzy

4

Hi again,

Could you please point me to the published results that you are mentioning? Is there an article that I could look into? Just to make sure what was their approach.

Cheers,

Jerzy

5

Thanks for your reply, The results I used for comparison come from this article: In-Beam PET Imaging in Carbon Therapy for Dose Verification (IEEE Transactions on Radiation and Plasma Medical Sciences, 2018). Here is the source website: In-Beam PET Imaging in Carbon Therapy for Dose Verification | IEEE Journals & Magazine | IEEE Xplore . Thank you very much for your help.

6

Hi @yang_xy

After looking into your input file and the paper I noticed a few issues with both. In my view, generally the paper does not describe the results clearly enough, but I will focus just on the Table II as this is what you were trying to reproduce with FLUKA. The Table II title says that it shows

Positron-Emitting Nuclei produced by a pulse of 259.5 AMeV 12C ions in the PMMA phantom

and to me that implies we need to take the number of nuclei of each isotope that we find at the end of irradiation profile and normalize it to 100 * 1E8 ions/second (as the paper defines 1E8 a single pulse). However, the numbers in Table II obtained with the simulations seem to be the same as the ones compared to the measurements quoted in Table I and these are defined as

the positron activity yields (...) when carbon beams impacted the PMMA phantom

and here I must admit I get a bit confused as I don’t know what the authors mean by positron activity yields.

Now coming to your input file:

First of all, you define the beam energy as 230 AMeV which does not correspond to any energy quoted in the paper. This is however a minor issue I think.

What is more important is your RESNUCLEI card will give the production rate Pas you do not assign any DCYSCORE card to it. Therefore, it will give you the P that you can find in the paper in equation (1) and (2) and in the end I don’t think this is what can be found in Table II in the Yield column. Initially I thought it is the case, but again, the paper is not very clear about it.

Then you define the irradiation profile with the IRRPROFI card:

Screenshot From 2026-01-15 15-52-26

that corresponds to 5 seconds beam time with 1e6 ions per second. According to the paper, the beam profile that you need is 100 pulses of 1 seconds each 1e8 ions/sec with 2 seconds break between them. So the profile would have to be defined with blocks like

Screenshot From 2026-01-15 15-54-54
Screenshot From 2026-01-15 15-54-54489×116 4.79 KB

repeated over and over until you reach 100 pulses.

Then there is your DCYTIMES card where you define t1: 0 and t2: 600 and I am not sure why would you need the t2as this is basically the time of 10 mins after irradiation and it does not appear anywhere in the analysis of the paper. You don’t use the t2 as I can see in your file so it is not a problem, but I would like to make sure that you are aware what you are doing with this card.

Then you have a bunch of USRBINwhen you score a single isotope activity at the t1:0which means exactly after the irradiation profile that you defie with IRRPROFIand I think this is correct. If you want the integrated activities for all the isotopes produced within the target region, you can also use RESNUCLEI and assign a DCYSCORE to it with time 0.

I tried to look at the activity at the end of the aforementioned irradiation profile of 100 pulses separated by 2 s pauses and then extract the number of generated nuclides N with the equation

N = A/lambda

where A is the activity at the end of irradiation and lambda is the decay constant of each nuclide, but still I was not able to reproduce the numbers from Table II.

If you can please help me understand better what the numbers in Table II actually mean, we can try together to reproduce the values with FLUKA.

Best,

Jerzy