Evaluation of Enhanced Leaf Modeling (ELM) In Eclipse V18: Impact on VMAT Plan Modulation, Delivery Efficiency, and Secondary Dose Verification
Abstract
Purpose
To evaluate the clinical impact of the Eclipse Version 18(V18) upgrade, specifically the implementation of ELM, on VMAT plan complexity, delivery efficiency, and dosimetric accuracy compared to the previous Version 15(V15).
Methods
A retrospective analysis was performed on two cohorts of VMAT plans: a pre-upgrade group (V15, n=78 plans) and a post-upgrade group (V18, n=78 plans). Both cohorts utilized the AcurosXB algorithm for dose calculation. Metrics evaluated included the Plan Complexity Index, Monitor Unit (MU), Patient Specific Quality Assurance (PSQA) with gamma pass rates at 2%/2mm, and secondary dose verification agreement using ClearCalc, utilizing Finite-Size Pencil Beam algorithm. Subgroup analyses were performed for 6MV, 6FFF, and 10FFF to assess the effect of energy. Statistical significance was determined using Welch’s t-test (p < 0.05).
Results
The transition to V18 resulted in a statistically significant reduction in average plan complexity, decreasing from 0.138 to 0.128 (p = 0.011). This reduction in modulation was most pronounced in plans utilizing 6MV energy (p = 0.001). An average reduction of 17 MU per field was observed in the post-upgrade cohort, indicating a trend toward higher delivery efficiency, though this did not reach statistical significance across the cohort (p = 0.366). Dosimetric accuracy remained high and stable, with average Gamma passing rates exceeding 99.7% in both groups (p = 0.486). Furthermore, the agreement between the Treatment Planning System and ClearCalc was nearly identical between versions (mean deviation of -1.51% vs. -1.53%; p = 0.597), confirming no systematic drift in dose calculation relative to the secondary algorithm.
Conclusion
The implementation of Eclipse V18 ELM reduces VMAT plan complexity and improves delivery efficiency while maintaining the high dose calculation fidelity seen in V15. The stability of the secondary check results demonstrates that the upgrade provides reduced modulation complexity without requiring adjustments to existing clinical quality assurance tolerances.