Patent ID: 7826593

Claim:
A radiation gantry comprising: a radiation generator for generating an input radiation beam; a radiation target; a beam scanning system for directing and scanning said input radiation beam onto said radiation target to form a narrow scanned pencil radiation beam having full width of half maximum of no more than 32 mm; a collimator for sharpening a penumbra of said narrow scanned pencil radiation beam, said collimator comprising at least one pair of collimator leaves, wherein: a penumbra-trimming portion of a collimator leaf facing an opposite collimator leaf of a collimator leaf pair is made of a first metal or a first alloy of said first metal having a first linear radiation attenuation coefficient and said first metal has a first atomic number according to the periodic table of the elements, said penumbra-trimming portion having a thickness in a range of about 10 to 50 mm in the direction of said narrow scanned pencil radiation beam; and a remaining support portion of said collimator leaf is made of a second metal or a second alloy of said second metal having a second linear radiation attenuation coefficient that is lower than said first linear radiation attenuation coefficient and said second metal has a second atomic number that is lower than said first atomic number.