Electron beam shaping device suitable for a machine for intraoperative radiation therapy IORT - Intra Operative Radiation Therapy-said machine comprising a mobile unit, provided with a linear accelerator having an electrons radiating head, and an operating control rack, which are wired connected to each other, said shaping device including a circular applicator, comprising a cylindrical tube and having a duct through which the electron beam is transmitted, adapted to be attached to said radiating head and which includes a proximal element, that is attached to said radiating head, and a distal element, adapted to be placed in contact with the area to radiate and that is attached to said proximal element, the shaping device being characterised in that it comprises: - a slab, which is removably attached to said distal element and which is provided with a hole corresponding to the duct of the circular applicator, - at least two planar elements, whereby each planar element comprises two overlapping plates (11, 12) which are attached to each other through first mechanical coupling means and whereby each planar element is attached to said slab in a variable position with continuity as a function of the attachment position of said first mechanical coupling means and of second mechanical coupling means, - said at least two planar elements being reciprocally arranged so as to be adjacent to each other and each planar element sliding with respect to another adjacent planar element through mechanical guide and slide means (12C, 12D), whereby the reciprocal arrangement of said at least two planar elements is adjustable so as to define an aperture of lower area than that of the section of the duct of said circular applicator, - said two overlapping plates (11, 12) being made of different materials, so that a first plate is made of a first sterilisable biocompatible material with a first atomic number and a second plate is made of a second sterilisable biocompatible material with a second atomic number larger than the first atomic number, whereby the second plate attenuates X-rays produced by the first plate. - Intra Operative Radiation Therapy-said machine comprising a mobile unit, provided with a linear accelerator having an electrons radiating head, and an operating control rack, which are wired connected to each other, said shaping device including a circular applicator, comprising a cylindrical tube and having a duct through which the electron beam is transmitted, adapted to be attached to said radiating head and which includes a proximal element, that is attached to said radiating head, and a distal element, adapted to be placed in contact with the area to radiate and that is attached to said proximal element, the shaping device being characterised in that it comprises: - a slab, which is removably attached to said distal element and which is provided with a hole corresponding to the duct of the circular applicator, - at least two planar elements, whereby each planar element comprises two overlapping plates (11, 12) which are attached to each other through first mechanical coupling means and whereby each planar element is attached to said slab in a variable position with continuity as a function of the attachment position of said first mechanical coupling means and of second mechanical coupling means, - said at least two planar elements being reciprocally arranged so as to be adjacent to each other and each planar element sliding with respect to another adjacent planar element through mechanical guide and slide means (12C, 12D), whereby the reciprocal arrangement of said at least two planar elements is adjustable so as to define an aperture of lower area than that of the section of the duct of said circular applicator, - said two overlapping plates (11, 12) being made of different materials, so that a first plate is made of a first sterilisable biocompatible material with a first atomic number and a second plate is made of a second sterilisable biocompatible material with a second atomic number larger than the first atomic number, whereby the second plate attenuates X-rays produced by the first plate.