  This report presents a design of a gantry for proton therapy based on the
concept of adiabatic transition. The use of fixed-field alternating gradient
magnets allows a large momentum acceptance and supports fast energy modulation.
The optical performance of the gantry has been analysed using a beam tracking
code. Several optimisations of the lattice and transition sections have been
investigated to reduce size and ensure applicability to pencil beam scanning.
Matching of the full energy range results in an increase in the size of the
gantry, but reduces the weight and cost significantly compared to those that
pertain to facilities in operation.
