I just played a very simple model for the proton beam dose in water, but the result is not as expected.
I set a 10cm x 10cm x 30cm water phantom. The incident proton beam is along the Z direction (the 30cm long dimension). I set the USRBIN to collect DOSE with 1mm voxel.
I shifted the primary 0.5 mm from (0,0), so the primaries will hit the center of the bin #(10,10) (index on the X-Y plane) as in the figure below.
The input is attached here (proton-water.inp (1.8 KB))
The figure below shows the dose along the beam direction from the incident bin #(10,10) and from the adjacent bins. The “Bragg peak” is roughly at the correct depth (maybe a little bit deeper), but the surface dose is so high.