Dear Gokhan,
When I do my analytical calculation for a 20 MeV proton in a 2 T field, I get a Larmor radius of 32.48223 cm.
Similarly, I get exactly the same result with my FLUKA simulation.
To automatize the calculations, you may need to implement an mgdraw.f routine, using the BXDRAW entry to record the coordinates of a particle crossing a boundary between two regions.
Cheers,
David