Synchronizing dynamic multileaf collimators for producing two-dimensional intensity-modulated fields with minimum beam delivery time.

PURPOSE Leaf motion synchronization of dynamic multileaf collimators (DMLC) for intensity-modulated radiotherapy (IMRT) is important in improving dose distribution and reducing "tongue-and-groove" effects for a prescribed intensity profile. Leaf synchronization could also be used in transforming a one-dimensional leaf-setting algorithm into a two-dimensional leaf-setting algorithm. In this work, we aim to develop a generalized leaf synchronization method for delivering IMRT with the minimized beam delivery time and the optimized subfield variations for a leaf-setting sequence. METHODS AND MATERIALS With the leaf synchronization procedure, all active MLC leaf pairs start and finish off a leaf sequence simultaneously. In this work, the MLC leaf pairs were synchronized under the condition that the resulting leaf sequence produces the desired intensity profile with the minimum beam delivery time. The parameter of the leaf synchronization function was determined through the least-square minimization of the area variations of all subfields within a leaf sequence. The leaf synchronization and optimization procedure were applied and analyzed for clinical relevant intensity profiles for treating the head-and-neck cancer patients using IMRT. RESULTS The total monitor units and the optimized beam delivery time of generating a two-dimensional intensity profile was proven through this work to be the global minimum of all leaf-setting sequences including the unsynchronized leaf-setting sequences. The optimized parameter for subfield variations of the synchronized leaf trajectories was found to be dependent on individual intensity profiles. For all our studied cases, the unsynchronized leaf trajectories always have significantly larger subfield variations than the synchronized leaf trajectories. CONCLUSION It is important and also feasible to synchronize and optimize dynamic MLC leaf motions while still keeping the total beam delivery time minimum for delivering arbitrary two-dimensional intensity-modulated fields.

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