Patent Number: 
Section: claims

1. A method for obtaining a shielding element for minimizing the penumbra of a scanning hadron pencil beam outside a target area, said hadron beam being scanned over the target area by an irradiation unit, said beam having a width (σ), the method comprising:(i) defining a closed or open contour of said target area;(ii) providing a block having a longitudinal thickness configured to block the passage of said hadron pencil beam and having a lateral surface perpendicular to said longitudinal thickness;(iii) forming an aperture of a shape similar to said contour of said target area, the aperture extending the length of the longitudinal thickness of said block in order to let through said hadron pencil beam, said aperture forming a longitudinal internal surface; and(iv) trimming said block so as to form a longitudinal external surface around said longitudinal internal surface, said longitudinal internal and longitudinal external surfaces delimiting a side wall, the side wall having a side thickness everywhere greater than at least once the width (σ) of the hadron pencil beam, and, in at least one location, less than five times the width (σ) of the hadron pencil beam. 2. The method for obtaining a shielding element according to claim 1, wherein the longitudinal external surface is similar to said longitudinal internal surface. 3. The method for obtaining a shielding element according to claim 1, wherein the method further comprises forming a support configured to attach said shielding element in said irradiation unit. 4. The method for obtaining a shielding element according to claim 3, wherein the support comprises an edge located on said longitudinal external surface formed during said trimming step. 5. The method for obtaining a shielding element according to claim 3, wherein the support comprises a base made in a low density material and having an aperture greater than or equal to said aperture of a shape similar to said contour and crossing said longitudinal thickness of said block, so as to let through said beam. 6. A shielding element obtained according to the method of claim 1. 7. An irradiation unit configured to scan a hadron pencil beam from a source over a target area, said irradiation unit comprising the shielding element according to claim 6, positioned between said source and said target area, so as to minimize the penumbra of the hadron pencil beam outside said target area. 8. A method for scanning a target area with a hadron pencil beam from a source, the method comprising placing the shielding element obtained according to claim 6 in an irradiation unit between said source and said target area, so as to minimize the penumbra of said hadron pencil beam outside said target area. 9. The shielding element obtained according to the method of claim 1, wherein the hadron pencil beam has a width (σ) of from about 3 to about 12 mm when exiting the irradiation unit. 10. The shielding element obtained according to the method of claim 1, wherein the longitudinal external surface is similar to said longitudinal internal surface. 11. A method of scanning a target area with a scanning hadron pencil beam, the method comprising:positioning a shielding element between a scanning hadron pencil beam irradiation unit and the tumor target area, the shielding element having a longitudinal thickness configured to block the passage of said scanning hadron pencil beam, the shielding element comprising:an aperture of a shape similar to an open or closed contour of said target area, the aperture extending the length of the longitudinal thickness of the shielding element in order to let through said scanning hadron pencil beam, said aperture forming a longitudinal internal surface of the shielding element,a longitudinal external surface around said longitudinal internal surface, said longitudinal internal and longitudinal external surfaces delimiting a side wall of the shielding element,wherein the side wall has a side thickness everywhere greater than at least once the width (σ) of the scanning hadron pencil beam, and, in at least one location, less than five times the width (σ) of the scanning hadron pencil beam. 12. The method of scanning a target area according to claim 11, wherein the scanning hadron pencil beam has a width (σ) of from about 3 to about 12 mm when exiting the scanning hadron pencil beam irradiation unit. 13. The method of scanning a target area with a scanning hadron pencil beam according to claim 11, wherein the longitudinal external surface is similar to said longitudinal internal surface. 14. A shielding element configured for use with a scanning hadron pencil beam irradiation unit whereby a scanning hadron pencil beam is scanned over a target area, said scanning hadron pencil beam having a width (σ), the shielding element having a longitudinal thickness configured to block the passage of said scanning hadron pencil beam, the shielding element comprising:an aperture of a shape similar to an open or closed contour of said target area, the aperture extending the length of the longitudinal thickness of the shielding element in order to let through said scanning hadron pencil beam, said aperture forming a longitudinal internal surface of the shielding element,a longitudinal external surface around said longitudinal internal surface, said longitudinal internal and longitudinal external surfaces delimiting a side wall of the shielding element,wherein the side wall has a side thickness everywhere greater than at least once the width (σ) of the scanning hadron pencil beam, and, in at least one location, less than five times the width (σ) of the scanning hadron pencil beam. 15. The shielding element according to claim 14, wherein the scanning hadron pencil beam has a width (σ) of from about 3 to about 12 mm when exiting a scanning beam irradiation unit. 16. The shielding element according to claim 14, wherein the longitudinal external surface is similar to said longitudinal internal surface.