Beam complexity and monitor unit efficiency comparison in two different volumetric modulated arc therapy delivery using automated planning

Abstract

Background: To investigate the beam complexity and monitor unit（MU）efficiency issues for two different volumetric modulated arc therapy (VMAT) delivery technologies for patients with left-sided breast cancer (BC) and nasopharyngeal carcinoma (NPC). Methods: Twelve left-sided BC and seven NPC cases were enrolled in this study. Each delivered treatment plan was optimized in Pinnacle 3 treatment planning system with Auto-Planning module for Trilogy and Synergy systems. Similar planning dose objectives and beam configuration were used for each site in two different delivery systems to produce clinically acceptable plans. Beam complexity was evaluated in terms of segment area(SA), segment width(SW), leaf sequence variability(LSV), aperture area variability(AAV), modulation complexity score(MCS) based on MLC sequence and MU. Results: With similar plan quality, the average SAs for Trilogy plans were smaller than those for Synergy plans: 55.5 ± 21.3 cm 2 vs. 66.3 ± 17.9 cm 2 (p<0.05) for the NPC cases, and 100.7 ± 49.2 cm 2 vs. 108.5 ± 42.7 cm 2 (p<0.05) for BC cases, respectively. The SW was statistically significant for two delivery systems (NPC: 6.87±1.95cm vs.6.72±2.71cm, p < 0.05; BC: 8.84±2.56cm vs.8.09±2.63cm, p < 0.05). LSV was statistically significant smaller for Trilogy (NPC: 0.84±0.033 vs.0.86±0.033, p < 0.05; BC: 0.89±0.026 vs.0.90±0.26, p < 0.05). The mean AAV was statistically significant larger for Trilogy than Synergy (NPC: 0.18±0.064 vs.0.14±0.037, p < 0.05; BC: 0.46±0.15 vs.0.33±0.13, p < 0.05). The MCS values for the Trilogy were higher than those for the Synergy: 0.14 ± 0.016vs. 0.12 ± 0.017 (p<0.05) for the NPC cases, and 0.42 ± 0.106 vs. 0.30 ± 0.087(p<0.05) for the BC cases. Compared with Synergy plans, the average MU for Trilogy plans were larger: 828.6±74.1MU and 782.9±85.2MU (p>0.05) for the NPC cases, and 444.8±61.3MU and 393.8±75.3MU (p>0.05) for the BC cases. Conclusions: The pinnacle 3 Auto planning system can optimize BC and NPC plans to obtain the same plan quality using Trilogy and Synergy systems. We found that this two systems resulted in different SA, SW, LSV, AAV and MCS. As a result, we suggested that beam complexity should be considered in providing further methodologies while optimizing VMAT auto planning.