Bidirectional leaf trajectory optimization approaches for dynamic delivery of intensity-modulated radiotherapy plans

Abstract

Purpose: Traditionally, unidirectional leaf-sweeping schemes have beenused for dynamic deliver y of intensity-modulated radiotherapy (IMRT) plans.This research investigates the potential benefits of bidirectional MLC-leaftrajectories to delivery efficiency and beam-modulation quality particularlywhen the available beam-on time is limited. Methods: This research relaxesthe unidirectional leaf-motion restriction and develops exact and heuristicleaf-sequencing approaches to obtain optimal bidirectional leaf trajectories.In par ticular, the proposed exact and heuristic approaches allow the MLCleaves to start from an arbitrary or pre-specified initial position and movefreely across the radiation field to modulate the desired fluence map. Theexact approach employs mixed-integer programming techniques to solve thearising non-convex optimization problem to a guaranteed optimality gap. Theheuristic methods exploit the special structure of the problem to obtain near-Medical Physics, 44 (6), June 20173205 2017 AAPM Annual Meeting Program 3205 optimal leaf trajectories, while requiring a significantly smaller computa-tional effort.