Hello
I’m working on proton therapy simulation using GATE code. At this stage, I obtained the proton fluence-depth chart in the water phantom. In high energies, especially 200 MeV in the flux chart, there is a sudden jump in the graph, which is completely abnormal. This mutation appears at about 100 MeV and higher. And it increases with increasing energy. Is there any reason? And why does not this mutation exist in low energies? I uploaded my chart in 200 MeV energy.
Many thanks
This looks like an artifact which doubles the fluence at a certain depth. Maybe a sum that is calculated and two y values are attributed to the same x value because x values are rounded?
But I also wonder how the fluence rises up to a depth of 10cm. How come that protons are "generated" within the target?
thanks for your answer
I have the same problem when I plot the fluence chart alone (without depth-dose).
A slight increase at about 10 cm is due to the protons' nuclear interactions and, consequently, the production of secondary particles.
Thanks
I think your simulation is correct. The mentioned jump is named Bragg pick and it is characteristic of the proton beams. It is used in proton therapy.
@Mojtabe Karbalae: Milad is talking about the jump in the fluence (blue dots) at around 22cm.
Thank you very much. Yes this is not my problem. I have a sudden jump in the proton fluence chart. (Blue diagram). Many thanks
The blue jump may be due to error. Repeat simulation with different history and seed number.
I repeated this simulation in the energy range of 5 to 200 MeV. And this jump appeared in energy 100 MeV and higher. (100, 125, 150, 175, 200MeV) and this mutation intensified with increasing energy. but I will test again for more confidence. Thank you so much
I think the observed increase is indeed the result of nuclear interactions which increase with proton energy. The main process is the interaction of protons with the ogygen O-atoms in water.
The following table shows the relative energy transfers for secondary particles for 150 MeV primary protons (%)
Protonen 57
Deuteronen 1,6
Tritonen 0,2
He-3 0,2
Alphas 2,9
Neutronen 20
Rückstoßkerne 1,6
geladene Sekundärteilchen total 64
Neutronen 20
Gammas 16
Tab. 9.1: Relative Energieüberträge von 150 MeV Protonen bei nuklearen Wechselwirkungen mit Sauerstoffkernen [NISTIR 5221].
The table is taken from my Book "Grundlagen der Strahlenphysik und des Strahlenschutzes", chapter 9.
A further tip. Please read Icru Report 63. you will find a lot of useful informations.
thank you so much. Do you think the sudden jump at about 22 cm is due to nuclear interactions? with respect
To be sure that we talk about the same facts. The decrease of your fluence curveat the end of their range is normal, because the protons are absorbed. So the decrease in your figure in the region of the Bragg peak is standard.
My problem is the enlarged fluence at the end of the fluence curve which can be observed for depth from 27 to 40 cm. When all protons are absorbed, fluence should be zero. I dont know your code. If your code works correct, the non zero fluence must be caused by proton interactions like nuclear reactions or by proton scattering by the protons in H2O molecules, which release the bound protons from water and enlarge the fluence.
The enlarged fluence above 25 cm must be a fault of your calculation code. The reason is, its impossible that nuclear reactions or elastic scattering in the Bragg peak region could transfer such high energies to the secondary protons, that they have still a range of about 15 cm.
Agrees with Hanno; This blue dot is some calculation artifact. It is much greater than initial fluence. Some singularity or simulation error as proton fluence is expected to be constant initially then decrease at Bragg Peak. Make step size small around that and check the variation to see the presence of other nuclear reactions. as told by @Hanno.
@Hanno Krieger @Munish Kumar: thank you very much for your helpful tips. I will check the code again. with respect
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