Depth-dose distribution for 182.5 MeV/u ⁴He impinging on a water phantom with a ripple filter in front (left vertical scale), as measured at HIT (red circles), and as calculated by FLUKA before (green line) and after (blue line) the improvements carried out in the last years. The green and blue symbols represent the fractional error of FLUKA versus the experimental results [225] (legend on the right vertical scale) before and after the improvements.