A leaf module for a multi-leaf collimator comprises a leaf unit and a leaf drive unit. The leaf unit comprises a leaf for shielding beams from a selected area. The leaf unit is mounted displaceably in an adjusting direction with relation to the leaf drive unit. The leaf drive unit is designed to displace the leaf unit linearly in the adjusting direction. The leaf drive unit comprises at least one drive mechanism which operates based on piezoelectric actuation, being designed such that the leaf drive unit thoroughly encloses the leaf unit within a plane being oriented substantially perpendicularly related to the adjusting direction. The multi-leaf collimator can comprise a plurality of leaf modules while being shaped as compact as possible. Both precise and stable adjustability of the leaf unit is achieved with the leaf module.
