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Leaf Motion Calculator Effect On Sliding Window IMRT Field Complexity and Plan Quality

E Laugeman*, E Pryser , M Schmidt , F Reynoso , Washington University School of Medicine in St. Louis, St. Louis, MO


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To evaluate the difference of the Varian Leaf Motion Calculator (VLMC) and the Smart LMC (SLMC) with (SLMC_JT) and without jaw tracking on field complexity and plan quality.

Methods: 25 clinical IMRT plans from five sites (Head and Neck, Breast, Lung, GYN, and Prostate) were originally calculated using the VLMC to determine leaf motions. The same optimized fluence was used to calculate leaf motions using the SLMC with and without jaw tracking enabled. The percent target volume that received the lower objective dose (VObj) used in optimization was used to evaluate the agreement of the final dose calculation to the optimized values. Plan quality was evaluated by recording PTV coverage by 95% of the prescription (V95%), OAR doses, and Modulation Factor (MF = MU/Dose). Field complexity was evaluated by recording Lost MU Factor (LMUF) and a Complexity Score (CS).

Results: The mean VObj for all VLMC plans was 53% compared to 90% for SLMC and 74% for SLMC_JT. Mean MF was 7.08 for VLMC plans, 6.55 for SLMC plans, and 6.75 for SLMC_JT plans. Mean PTV coverage increased to 99.4% with SLMC compared to 98.3% with VLMC. OAR doses increased for SLMC when compared to VLMC, however, SLMC_JT had equivalent or lower OAR doses. LMUF decreased an average of 8.4% and 6.0% per field when using SLMC and SLMC_JT, respectively when compared to VLMC. More importantly, the CS decreased by 11% for both SLMC and SLMC_JT.

Conclusion: SLMC reduced the complexity of sliding window IMRT fields resulting in a higher max dose and an overall higher OAR doses. SLMC_JT saw a similar reduction in field complexity, but OAR doses were similar to VLMC plans. The differences in final dose distributions warrants using optimization objectives specific to the LMC used and strongly supports SLMC for decreased field complexity.


Intensity Modulation, MLC, Treatment Planning


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

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