Evaluation of Dosimetric Difference between Eclipse 16.1 and Eclipse 18.1 for SRS/SBRT Planning
Abstract
Purpose
To evaluate Eclipse version 18.1 (EV181) with the new Enhanced Leaf Model (ELM) and its impact on SRS/SBRT planning compared with Eclipse version 16.1 (EV161).
Methods
A phantom study was performed in EV181 to compare calculated with measured dose with various MLC shapes using dose plane Gamma pass rate(GP%). Calculated dose differences between EV161 and EV181 were first evaluated with Static Asymmetric MLC shapes (SAMLC) using dose plane GP%, then with a total of 10 SRS & SBRT cases treated in 2025 including 3 multi-targets (MT) SRS patients, 2 single target (ST) SRS patients and 5 ST SBRT patients. Treatment plans were optimized in EV161 and calculated in EV161 and EV181 with 1mm dose grid size (DGS) for SRS and 2mm DGS for SBRT. PTV conformity index (CI), Gradient index (GI) and plan Dmax from EV161 and EV181 were compared using paired t-test.
Results
In phantom study, GP% (2%2mm, 0% threshold) for all dose planes are 99.5%±0.6% indicated great match between calculated and delivered dose in EV181. GP% between EV161 and EV181 with SAMLC were 100% in both transverse and coronal dose planes. For patients’ plans, CIs calculated in EV161 (1.11±0.01) increased significantly (p= 0.001) in EV181 (1.29±0.05), along with Dmax changed from an average of 119% (EV161) to an average of 122%(EV181) signifying the dose difference introduced by ELM. GI changed from 5.3±7.6 (Ev161) to 5.7±8.3 (EV181) demonstrated dose 50% or higher were all impacted while may not be statistically significant (p=0.1). SRS/SBRT plans were highly impacted due to high plan modulation and smaller field size. MTSRS plans were more impacted than STSRS.
Conclusion
ELM in EV181 impacted dose around MLC edge and may lead to large dose difference for SRS/SBRT plans, therefore EV161 Plans may need to be re-optimized to achieve the same planning goal in EV181.