Fig. 5: Spread-out Bragg peak (SOBP) profiles from a SpeleoFilter.
From: Range-compensated pencil beam scanning proton Arc therapy: a feasibility study

Uniform depth dose profiles optimized to provide a SOBP range of 3 cm, 5 cm, and 7 cm along the central axis. Each profile was simulated in Geant4 for a uniform field delivered using pencil beam scanning.