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Development of Bidirectional Leaf Sequencing Delivery Technique for Varian Medical Linear Accelerator

R Kamal1*, G Singh1 , A Oinam2 , D Thaper1 , V Kumar1 , B Handa1 , (1) Centre for Medical Physics, Panjab University, Chandigarh, (2) Department of Radiotherapy, PGIMER, Chandigarh


(Sunday, 7/14/2019) 3:30 PM - 4:00 PM

Room: Exhibit Hall | Forum 7

Purpose: To indigenously develop bi-directional non-monotonous segmented leaf sequence (NSLS) MLC delivery technique compatible to Varian MLC for non-splitted IMRT fields reducing TotalMU and number of segments simultaneously to minimize total treatment time.

Methods: Five patients of carcinoma in Lung were selected retrospective and Eclipse version 11.0 TPS (Varian Medical Systems, Palo, Alto, USA) is used to generate optimal fluence and hence MLC fields using MSS LMC algorithm for IMRT plans. The optimal fluence is exported and used as input to generate segmented MLC fields as per criterion given by Xia, Siochi, Engel and indigenously developed equally spaced (ES) reducing level, (NSLS) algorithms for 4 – 10 intensity levels using MATLAB version 2011b (The MathWorks, Natick, MA). These MLC fields are imported into plans with same field setup and final dose is recalculated in TPS. A plan scoring index (PSI) is defined to compare quality of different plans for same patient quantitatively.

Results: NSLS algorithm is compared to MSS, Siochi, Engel, Xia, ES algorithms for 4 – 10 intensity levels. The IMRT plan generated using proposed NSLS resulted in best PSI amongst all leaf sequencing algorithms for all cases studied whereas plan generated using Xia resulted in worst PSI in most of the cases.

Conclusion: The proposed algorithm allows bidirectional delivery in Varian which is not available commercially and has the lowest MU as well as total number of segments with equivalent plan quality in terms of conformity and coverage indices and clinically insignificant changes in OAR doses. The additional advantage includes reduced body scatter dose and interplay effect compared to unidirectional delivery.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by DST-PURSE Grant


MLC, Intensity Modulation, Monitor Unit Calculations


TH- External beam- photons: General (most aspects)

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