Conversion device for converting treatment beam for treating lesion of subject

A conversion device for converting a treatment beam to treat a subject's lesion, comprising:

• a collimator unit on which the treatment beam is incident and in which a plurality of slits are formed, wherein the treatment beam includes a charged particle beam;
• and
• a scattering unit that scatters the treatment beam that has passed through the collimator unit, wherein the scattering unit includes a first scattering unit and a second scattering unit located between the first scattering unit and the lesion, and the first scattering unit and the second scattering unit respectively include a plurality of scattering units having respective levels of scattering and being selectable by a user.