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Beam Complexity and Monitor Unit Efficiency in Volumetric Modulated Arcs Therapy for Left-Sided Breast and NPC Plans

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c li

c li*, J Lu , Y Yin , Shandong Cancer Hospital Affiliated to Shandong;Shandong Cancer Hospital, Jinan, Shandong


SU-I-GPD-T-338 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To investigate the beam complexity and MU efficiency issue for two methods of VMAT delivery technologies implemented in Pinnacle automated inverse treatment planning system for patients with left₋sided breast cancer and NPC.

Methods: Ten left-sided breast and seven NPC cases were studied. Each delivered treatment plan was optimized with the Auto-Planning module using Trilogy system (Varian Medical Systems, Palo Alto, CA) and Synergy system (Elekta Ltd, Crawley, UK) respectively. Auto-Planning was used to produce clinically acceptable treatment plans, we used the similar planning dose objectives and beam configuration for each site in two different delivery systems, as a result, the coverage for PTVs and dose constrains for OARs were as same as possible. Beam complexity was evaluated in terms of segment area(SA),modulation complexity score(MCS) based on MLC sequence and MU.

Results: With similar plan quality, the average segment areas (expressed in mean ± SD) for the Trilogy plans were smaller than those for the Synergy plans: 55.5 ± 21.3 cm 2 vs. 66.3 ± 17.9 cm 2 (p<0.05) for the nasopharynx cases, and 100.7 ± 49.2 cm 2 vs. 108.5 ± 42.7 cm 2 (p<0.05)for the breast cases, respectively;The average MU was 444.8±61.3MU for Trilogy and 393.8±75.3MU for Synergy among breast patients and 828.6±74.1MU for Trilogy and 782.9±85.2MU for Synergy among NPC patients.The MCS values for the Trilogy plans were larger than those for the Synergy plans: 0.14 ± 0.016vs. 0.12 ± 0.017 (p<0.05) for the nasopharynx cases, and 0.42 ± 0.106 vs. 0.30 ± 0.087 (p<0.05) for the breast cases;

Conclusion: Similar plan quality can be achieved with two delivery systems (Trilogy and Synergy) optimized by the Pinnacle Auto-Planning. Two systems resulted in much different SA and MCS. The beam complexity difference could be considered in auto-plan designing.

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