Minimizing the number of segments in a delivery sequence for intensity-modulated radiation therapy with a multileaf collimator

This paper proposes a sequencing algorithm for intensity-modulated radiatio n therapy with a multileaf collimator in the static mode. The algorithm aim s to minimize the number of segments in a delivery sequence. For a machine with a long verification and recording overhead time (e.g., 15 s per segmen t), minimizing the number of segments is equivalent to minimizing the deliv ery time. The proposed new algorithm is based on checking numerous candidat es for a segment and selecting the candidate that results in a residual int ensity matrix with the least complexity. When there is more than one candid ate resulting in the same complexity, the candidate with the largest size i s selected. The complexity of an intensity matrix is measured in the new al gorithm in terms of the number of segments in the delivery sequence obtaine d by using a published algorithm, The beam delivery efficiency of the propo sed algorithm and the influence of different published algorithms used to c alculate the complexity of an intensity matrix were tested with clinical in tensity-modulated beams. The results show that no matter which published al gorithm is used to calculate the complexity of an intensity matrix, the seq uence generated by the algorithm proposed here is always more efficient tha n that generated by the published algorithm itself. The results also show t hat the algorithm used to calculate the complexity of an intensity matrix a ffects the efficiency of beam delivery. The delivery sequences are frequent ly most efficient when the algorithm of Bortfeld et al. is used to calculat e the complexity of an intensity matrix. Because no single variation is mos t efficient for all beams tested, we suggest implementing multiple variatio ns of our algorithm. (C) 2001 American Association of Physicists in Medicin e.