  In intensity-modulated radiation therapy, optimal intensity distributions of
incoming beams are decomposed into linear combinations of leaf openings of a
multileaf collimator (segments). In order to avoid inefficient dose delivery,
the decomposition should satisfy a number of dosimetric constraints due to
suboptimal dose characteristics of small segments. However, exact decomposition
with dosimetric constraints is only in limited cases possible. The present work
introduces new heuristic segmentation algorithms for the following optimization
problem: Find a segmentation of an approximated matrix using only allowed
fields and minimize the approximation error. Finally, the decomposition
algorithms were implemented into an optimization programme in order to examine
the assumptions of the algorithms for a clinical example. As a result,
identical dose distributions with much fewer segments and a significantly
smaller number of monitor units could be achieved using dosimetric constraints.
Consequently, the dose delivery is more efficient and less time consuming.
