Dosimetric Equivalent Machines and Mlc Configurations with Enhanced Leaf Model (ELM)
Abstract
Purpose
Enhanced Leaf Model (ELM) introduced in Varian Eclipse v18 has demonstrated improved commissioning efficiency and consistency with equivalent or superior dose calculation accuracy such as for HyperArc. This study investigated the feasibility of using ELM to configure MLC parameters for dosimetric equivalent machines.
Methods
Three Varian TrueBeam linacs with Millennium MLC were beam-matched during commissioning. A set of optimal DLG_v16 and Transmission was fine-tuned with dynamic chair patten and used for all three linacs in Eclipse v16. In Eclipse v18, machine-specific DLG_ELM and Transmission were derived from sweeping gap fields measurements for each linac and a set of optimal DLG_ELM and Transmission was also determined and used for all three linacs for dosimetric equivalent machine purpose. Gamma analysis was performed for dynamic chair patten calculated in Eclipse and measured on each linac for 6FFF and 10FFF.
Results
With the optimal DLG_v16 and Transmission set used for all three linacs, gamma results (2mm-2%-10% threshold) were > 99.8%, 98.6%, and 98.4% for 6FFF and > 99.9%, 99.8%, and 99.8% for 10FFF. With machine-specific DLG_ELM and Transmission for each linac, gamma results were > 88.2%, 92.0%, and 92.7% for 6FFF and > 99.7%, 99.7%, and 99.8% for 10FFF. With the optimal DLG_ELM and Transmission set used for all three linacs, gamma results were > 92.9%, 91.6%, and 92.3% for 6FFF and > 99.8%, 99.1%, and 99.4% for 10FFF. Gamma analysis was equivalent for 10FFF. While gamma analysis for 6FFF indicating DLG_ELM is inferior to DLG_v16, the passing rate for 3mm-3% was still > 95%.
Conclusion
Enhanced Leaf Model accounts for MLC rounded leaf‐end and leaf thickness for dose calculations. While it was designed to derive DLG_ELM and Transmission for each specific linac, it is possible to determine an optimal set for all machines and take advantage the convenience of dosimetric equivalent machines.