| CPC A61N 5/1045 (2013.01) [G21K 1/046 (2013.01)] | 15 Claims |

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1. A leaf assembly for a multi-leaf collimator, the leaf assembly comprising:
a leaf; and
a leaf nut removably mounted within a profile of the leaf, the leaf nut comprising a threaded hole for receiving a leaf actuator screw oriented along a first axis in a plane of the leaf, the leaf nut being mounted within the leaf such that relative movement between the leaf nut and the leaf is prevented both linearly along the first axis and rotationally about the first axis, wherein movement of the leaf nut relative to the leaf along a second axis is limited between a first and second position along the second axis, wherein the second axis lies across the first axis and is in the plane of the leaf.
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