![]() ![]() However, the SF-MLC has a noticeably sharper penumbra, which we attribute to its position further from the source. We attribute this, at least in part, to the rounded ends of the SF-MLC leaves. We observe that the 50% isodose line oscillates around the PFE with greater amplitude for SF-MLC. The amplitude of the oscillations of the 50% isodose line about the PFE and the penumbra width as determined by the 20%, 80%, and 90% isodose lines was examined. They also have the advantage that for an ideal field shaping system the resulting isodoses are concentric perfect circles, a well-defined basis for evaluation. Circular fields, centered on axis and off axis, were used because they produce a range of "angles of approach" between the MLC leaves and the PFE. The ability of each MLC to conform isodose lines to a prescribed field edge (PFE) was evaluated using film dosimetry. The MLC designs evaluated were: a "single-focused" MLC (SF-MLC) mounted below the jaws, and a "double-focused" MLC, which is a complete replacement for the lower jaws. We present the results of measurements designed to compare two different multileaf collimator (MLC) designs using a novel evaluation technique. ![]()
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