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The performance of segmentation algorithms used in IMFAST for "step & shoot" IMRT
treatment delivery is evaluated for three head and neck clinical treatments of different
optimization objectives. The segmentation uses the intensity maps generated by the
in-house TPS PLANUNC using the index-dose minimization algorithm. The dose optimization
objectives include PTV dose uniformity and dose volume histogram-specified critical
structure sparing. The optimized continuous intensity maps were truncated into five
and ten intensity levels and exported to IMFAST for MLC segments optimization. The
MLC segments were imported back to PLUNC for dose optimization quality calculation.
The five basic segmentation algorithms included in IMFAST were evaluated alone and
in combination with either tongue and groove/match line correction or fluence correction
or both. Two criteria were used in the evaluation: treatment efficiency represented
by the total number of MLC segments and optimization quality represented by a clinically
relevant optimization quality factor. We found that the treatment efficiency depends
first on the number of intensity levels used in the intensity map and second the segmentation
technique used. The standard optimal segmentation with fluence correction is a consistent
good performer for all treatment plans studied. All segmentation techniques evaluated
produced treatments with similar dose optimization quality values, especially when
ten-level intensity maps are used.