A simple method to control aspects of fluence modulation in IMRT planning

Many inverse-planning algorithms and commercial systems generate intensity- modulated beam profiles that have considerable structure. This is the desir able outcome of the quest for high dose-space conformality. However, when t hese profiles are realized experimentally using the dynamic multileaf colli mator (DMLC) method of delivery the monitor-unit efficiency can be quite sm all. with unwanted consequences. Also the interpretation of these fields le ads to the generation of small field segments. again with undesirable conse quences. In this note it is shown that the features of beam-space can be us er-controlled to minimize these problems. There is a tradeoff between obtai ning desirable features in beam-space and high conformality in dose-space.