Improving delivery of segments with small MU in step-and-shoot IMRT.

The purpose of this study is to describe four new delivery schemes for intensity-modulated radiation therapy (IMRT). In the first two schemes the order in which segments are delivered is varied from fraction to fraction. The last two delivery schemes employ fixed order of segments. The obtained results indicate that the suggested approaches can significantly reduce the so-called "overshoot" and "undershoot" phenomena and the associated discrepancies between planned and delivered monitor units.