Optimal setting of multileaf collimators in stationary beam radiation therapy.

The new generation of high resolution double focused multileaf collimators is an important step towards true three-dimensional radiation treatment techniques. The principal advantages include increased flexibility in beam shaping and dose delivery using static radiation fields as well as the possibility to do conformation therapy employing dynamic computer controlled patient individual collimation in each CT slice and lateral dose plan. Beside the increased efficiency and flexibility and reduced set-up time, it is shown that multileaf collimation will often reduce the treated volume by as much as 20% or more in single fields and more than 30% when multiple fields are used instead of ordinary rectangular fields. When compared to conventional beam blocks the greater simplicity and flexibility will probably increase the use of individualized blockings by about the same percentages. The optimal rotation and setting of a multileaf collimator for static radiation fields is derived both for convex and for convex concave target volumes. Generally, the smallest cross-section or diameter of the target should be aligned with the direction of motion of the leaves.