I am a very new user of Fluka, and I am using Flair for my simulations. I am trying to simulate an Ir-192 source used for high-dose-rate brachytherapy to understand the dose distribution in depth through various materials. As a first approach, I simulated two adjacent layers of water (I simulated two layers since in future I will change the material of one of them). Since I am not interested in the temporal profile of the source but only in the dose behavior in depth, I replaced the source with a photon beam having an energy equal to the average energy of the source itself (390 keV). However, from the 1D-projection plot, I noticed that the dose in depth remains essentially constant, whereas I would expect a decreasing trend due to photon attenuation.
If you limit the 1D Protection only to the center bins in the Xand Y axes (or use the 1D Max plot type), the decrease of dose deposition along the Z axis becomes more noticeable.
Thank you for your help. I was expecting a curve with a steeper decrease since dose gradients in brachytherapy are very high. In fact, what I was simulating was a photon beam with energy of 390 keV but with a specific propagation direction. The difference compared to a radioactive source is that the latter has isotropic emission and a specific spatial distribution (in my case cylindrical). By modifying the angular distribution in the beam card from “flat” to “isotropic” and inserting in the beampos card “cyli-vol,” with the addition of another beampos card with type “negative,” the depth dose curve indeed shows a very rapid decrease: in 2 cm the reduction is about 80%, as I expected.
Thanks again for your time!
Cheers,
Laura