In intensity modulated radiation therapy (IMRT), intensity maps are computed from prescribed doses to target volumes, adding dose restrictions to the surrounding tissues. Those intensity (fluence) maps are discretized into matrices of natural numbers and translated to sequences of multileaf collimator (MLC) leaf movements, which will finally deliver the computed x-ray intensities. A unidirectional leaf sequencing algorithm that controls the shape of the segments and reduces leaf motion time for step-and-shoot dose delivery is presented. The problem of constructing segments in controlling its shape was solved by synchronizing right leaves motion. This is done without increasing the number of segments, or the total number of monitor units, and taking into account the unidirectional leaf motion and the interleaf collision constraints. The method was tested using random matrices and a clinical case planned with the PCRT 3D(R) planning system. Compared to other unidirectional leaf sequencing methods, the proposed algorithm performs very similarly. But, in addition, the segment shape control produces segments with smoother outlines and more compact shapes, which may help to reduce MLC-specific effects when delivering the planned fluence map. Finally, as a result of imposing unidirectionality, this algorithm can be extended for sliding window segment generation.
In intensity-modulated radiation therapy (IMRT), fluence matrices obtained from a treatment planning system are usually delivered by a linear accelerator equipped with a multileaf collimator (MLC). A segmentation method is needed for decomposing these fluence matrices into segments suitable for the MLC, and the number of segments used is an important factor for treatment time. In this work, an algorithm for reduction of the number of segments (NS) is presented for unidirectional segmentations, where there is no backtracking of the MLC leaves. It uses a geometrical representation of the segmentation output for searching the key values in a fluence matrix that complicate its decomposition. The NS reduction is achieved by performing minor modifications in these values, under the conditions of avoiding substantial modifications of the dose-volume histogram, and does not increase in average the total number of monitor units delivered. The proposed method was tested using two clinical cases planned with the PCRT 3D treatment planning system.
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