Siemens linacs use multileaf collimators (MLCs) that move in an arc such that the flat faces of the leaf ends are always in the same plane as the radiation focus. An effect of this is that the magnification of the leaf end projection the isocentric plane normal to the collimator rotation axis varies with the drive position of the leaves. This effect is quantified theoretically and empirically verified. A method is introduced for assessing the importance of the effect for a particular MLC pattern. The significance of the effect is discussed.
Buckle AH. Varying MLC end projection size: an effect of the double-focused Siemens multileaf collimator. Phys. Med. Biol. 51 (2006) N147-N155.
Andrew Buckle, NGH Unit, Newcastle upon Tyne. Tel: +44 (0)191-233-6161.
Regional Medical Physics Department, Freeman Hospital, Newcastle upon Tyne, NE7 7DN, UK.
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