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A MLC Leaf Sequencing Algorithm Restricted by the Shape of Aperture for IMRT

J Jing1,2 , H Lin1 , B Zhang1 , J Chow2*, (1) Hefei University of Technology, Hefei, China, (2) Princess Margaret Cancer Centre, Toronto, ON


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: The presence of a large number of beam segments with complex shapes in intensity-modulated radiotherapy (IMRT) can increase the multileaf collimator (MLC) artefacts when generating the fluence map. To regulate the shape of the segmental field between adjacent apertures, an improved leaf-sequencing algorithm is proposed and verified by clinical fluence map experiments.

Methods: In the leaf-sequencing algorithm, the MLC aperture is subjected to the distance between adjacent rows. As the distance decreases, the distance parameter d becomes smaller. The value of d can be optimized in the treatment planning to omit the beam segments having low-weight monitor unit, and very small MLC apertures. A house-made integrated multi-functional leaf-sequencing computing system based on the proposed algorithm was created, and used to perform calculations and analyses. All treatment plans in this study were created using the ARTS treatment planning system (TPS).

Results: The procedure for determining the delivery sequence of the fluence map in spinal cord IMRT was used to verify the proposed leaf-sequencing algorithm. Fluence maps generated by the algorithm restricted by the shape of the aperture were validated and compared to fluence maps produced by the ARTS TPS using a benchmark algorithm. Results showed that the algorithm had a good agreement in the number of beam segment (NS) and total number of monitor unit (TNMU) compared to the benchmark. In addition, this algorithm can keep the MLC segmental fields in a compact pattern.

Conclusion: By comparing and analysing results of the NS and TNMU with those generated by the benchmark, our proposed algorithm restricted by the shape of the aperture performed well, and produced segmental fields with more compact shapes. This helps to reduce the artefacts on the fluence maps generated by the MLC in IMRT delivery.


MLC, Intensity Modulation


TH- External beam- photons: treatment planning/virtual clinical studies

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