IORT device (10) for radiotherapy treatment of cancer patients, comprising a source of particles, an accelerating device (11), which sends a beam of particles (12) on a target (14) through an applicator (15), a scattering filter (16), which allows the distance between the source of particles and the target (14) to be kept within a range compatible with the use of IORT devices (10) in standard operating rooms, and an optical system for collimating the beam of particles (12), which is placed between the scattering filter (16) and the applicator (15)； specifically, the optical collimating system of the beam of particles comprises a primary screen (17), configured to shield the radiation produced by the scattering filter (16), a secondary screen (18), configured to shield the photons produced on the primary screen (17), and a collimating apparatus (19), which provides for housing the monitor chambers (20).
