The generation of intensity-modulated fields for conformal radiotherapy by dynamic collimation

An algorithm has been developed to calculate the collimator jaw motions required to generate intensity-modulated fields far use in conformal radiotherapy. The dynamic technique allows arbitrary intensity profiles to he generated using a single unidirectional sweep of the collimators. The collimator jaws have independent motion, so that an aperture of variable width is scanned across the field. The algorithm has the form of a constrained optimization problem and jaw motions are optimized such that the treatment time for the field at a given dose rate is minimized. The application and results of this technique are presented, and it is shown that this approach provides an efficient practical implementation of conformal radiotherapy plans based on the use of intensity-modulated fields. The technique can be extended to 3 D treatment plans and fields through the use of computercontrolled multileaf collimators.