Dose USRBIN in x-ray beam

Scoring
1

Hello everyone,
I’m trying to simulate an x-ray beam and then calculate the kerma at different distances. To do this I am using USRBIN for the dose. Once the dose value has been obtained in the desired region, if I understood correctly, this is expressed in [GeV*cm^3/g]. so I just have to multiply by the conversion factor GeV/g ->J/kg and divide by the volume considered right?

Thank you

3

Hi Andrea,

Can you share your input?

The answer depends on a couple of things:

  1. which option are you specifying for USRBIN (“generalized particle”)? DOSE or ENERGY?
  2. are you applying a mesh or scoring an entire region?

Once you provide the input I can let you know how to convert it to the units you require.

Stefano

4

First of all thank you for your availability. I am attaching the file. Another thing, my goal is to simulate an x-ray beam I don’t know if the code is right. I would also like to understand how to generate a rectangular and not circular beam.
Tubo_raggixPMMA3.inp (5.2 KB)

Thank you

5

Hi Andrea,

thank you for the input. Are you using flair (the graphical interface for FLUKA)? I recommend this, as it is going to make creating the input much easier.

There seems to be a few problem in your input, so I will try to address some of the issues but I strongly recommend you look at the FLUKA beginner course which is available online (link).

Let’s start with the photon source. You currently have specified a photon beam with a 0.2 rad angular dispersion, but you didn’t specify an energy. Right now it is defaulting to 200 GeV photons, well above the X-ray regime. To answer your question, it is possible to simulate a rectangular beam (which is actually what your input is currently doing). You appear to be using a SOURCE card, but in the absence of a custom source routine this is not needed (since you are looking to simulate a fairly simple geometry, I don’t think you will need this).

The beam is incident on a polymer target, and then you are using a REGION scoring with the PHOTON option on a series of targets placed around the polymer. (In your initial question you mentioned that you wanted to measure the kerma at different distances; but this simulation appears to be studying the angular distribution rather than the distance dependence.) The result of this scoring will be a fluence, i.e. the integrated track length of photons per unit volume (units of 1/cm^2). However, because FLUKA does not know the volume of the arbitrary region you have used, it will assume a volume of 1cm^3. It is your task after to divide the quantity by the volume of your actual scoring region. However, if you are interested in kerma, this is not the scoring you want. I suggest you use DOSE instead of the PHOTON fluence. I further suggest you use a cartesian X-Y-Z mesh, but that’s just because it will take care of the volume for you.

So, to summarize, the input is currently not doing what you are wanting to do. My suggestions are:

  1. Use Flair for a more straightforward initialization of your geometry
  2. Look at the FLUKA beginnner course slides, specifically the ones regarding sources and scoring
  3. Fix the beam energies and spread (in Flair it will be trivial)
  4. Ensure that the geometry of your setup is correct (angular distribution of kerma vs distance dependence)
  5. Use a DOSE scoring (or ENERGY scoring, taking care to further divide by the density of your scoring region)

I hope this helps.

Stefano

1 Like
6

Thanks for the reply. I was probably imprecise. I’m already using FLAIR and the beam energy is not set because it is defined in the source routine (that’s why I inserted source in the code). I’m using a source routine to define the x-ray spectrum to simulate, I don’t know if it can be done more easily. Finally another question if I want to know the number of particles in a region I can use USRBDX right?

Thanks again

7

Hi Andrea,

thank you for the clarification. That makes more sense. In the source routine you can also set the position of the emitted particles, so you can simulate a rectangular bin. If you have a complex X-ray spectrum, then the source routine is the best option to specify the beam. You may also specify the shape of the beam in the BEAM card, but then be careful to not override it in your source routine.

If you are confident in your source and geometry of the scored region, then the only thing that needs fixing is the scoring option. USRBDX score boundary crossing, so it is not the most appropriate for this purpose. The fluence (the one you already specified, using PHOTON on USRBIN) is going to give you a measure of how many particles cross that region. Given your initial question, I would also add a DOSE scoring, taking care to divide by the volumes of the scoring regions. Then you may convert this to SI units to get the score you need.

Let me know if this is of help,

Stefano

1 Like
8

Hi @andrea.apollon,

it was brought to my attention that the SOURCE routine will override all the beam parameters except for the energy. Therefore, as I suggested above, you should specify the beam profile directly in the source routine.

Let me know if there is anything else I can help with

Stefano