Scoring PET signal in proton therapy

Dear FLUKA experts,

I’m trying to score PET signal (activity) in proton therapy.
Without using a PET machine, I’d like to directly score the PET signal into a water phantom, namely the true PET signal.
Moreover, I also want to score the PET signal for different time period. That is, for 30s, 1min, and 10 min after the proton beam was delivered.
Attached is the .inp file that I have constructed. I’m not sure whether it meets my goals.
In particular, for scoring the PET signal, should I use DETECT or USRBIN? And for different time period, is it correct to use DCYTIMES? How could I score the above three different time periods by running the simulation for one time only?

Best regards,
Kaiwen Li

PET_Proton.inp (1.2 KB)

Dear Kaiwen,

It looks to me, that it would be better to score the activity of the beta+ decaying isotopes, rather than the electron/positron/photon fluences.

Please have a look at the following lecture, especially on the Activation part starting on slide 26.


Dear David,

Thanks for your reply!
I followed your advice and another topic

to score the activity of C11 and O15, but the output of these two are zero. I do not know where was wrong. I would appreciated it a lot if you could help check the attached .inp file.

And some more questions,

  1. what is the definition of activity (for C11 and O15) here?
  2. since the goal of mine is to obtain the PET signal (e+e- to gamma), but here is to score C11 and O15, and the e+ will move for some distance after the decay of C11 and O15 happens, is it accurate enough?
  3. for scoring the activity of C11 and O15, when I set USRBIN type to X-Y-Z (BIN 22 and 23), It runs with errors, why?
  4. for the RADDECAY card, when I set the decay to Active, it runs with errors, I can only use semi-analog mode. why?

proton_pet.inp (2.1 KB)

Moreover, my goal is to obtain the following figure (solid line, the Activity)

Dear @kwlibuaa,

I will take a close look at your issue and get back to you asap.


Dear @kwlibuaa,

You are mixing some things up. Please take a second look to the lecture shared earlier by David in order to understand the differences and scope of the two radioactive decay simulation modes: semi-analogue and activation.

In your input, you have requested semi-analogue mode, but at the same time linked the scorings with decay times meant to be used only for activation mode. Inevitably, all your results are zero.

In your case, you want to use the activation mode since your goal is to quantify activation at given times during or after irradiation. When you select activation mode, you see that you get an error (question 4.). This is because in the IRRPROFI card, where you must specify the intensity and time structure of you beam, an intensity of 0 primaries per second during 100000 seconds was chosen, which makes no sense. Please provide a sensible intensity. Once these 2 changes are implemented, your simulation should run successfully.

Regarding your questions:

  1. The definition of activity is number of disintegrations per unit time. Since you are scoring activity in a mesh using a USRBIN, the unit of the results you get is Bq/cm3 per primary. See Note 10 in the USRBIN entry of the manual.
  2. Indeed positrons will travel some distance before they annihilate. If you want to score activity (as it seems from you latest post) you don’t care about this. But this effect is already accounted for by the code in order to accurately emit the gammas, so if at some point you want to study them you can do so. Just keep an eye on your transport and production thresholds (see lecture below).
  3. Scoring Activity and using a USRBIN of type X-Y-Z are not compatible. You must use the X-Y-Z point type, as you did.
  4. Already addressed.

Hope it helps.

Kind regards,

Dear Francisco,

Thank you very much for your detailed answer!
I am very clear with most of the above questions.
One more question, what is the relationship between the particle intensity of the IRRPROFI card and the primary particle number of the START card in my case? As I increased the primary particle number of the START card, the oscillation of the C11 and O15 intensities were mitigated. But when I changed the particle intensity of the IRRPROFI card, the oscillation of the C11 and O15 intensities still remained.

Best regards,

None: the first is a physical normalization factor, with no impact on the statistical quality of your results, while the second rules the latter, which explains your findings.