Evaluation of the accuracy of an enhanced MLC leaf model for Linac-based stereotactic radiosurgery

For LINAC-based stereotactic radiosurgery (SRS) treatments, the binary MLC models utilizing single dosimetric leaf gap (DLG) parameters in Eclipse versions prior to v18 can result in imperfect agreement between measured and calculated doses, increased commissioning complexity, and user-dependent variability. This study aims to evaluate the efficiency and accuracy of the enhanced leaf model (ELM) in Eclipse version 18.0, which incorporates the actual rounded-end MLC design in dose calculations.

ELM parameters were determined from measurements and configuration in a test Eclipse v18.0 system for an Edge LINAC with High Definition MLC (HDMLC) and a TrueBeam LINAC with the Millennium 120-leaf MLC (M120). The anisotropic analytical algorithm (AAA) was used to calculate doses for both 10FFF and 6FFF energies. The v18 ELM model was compared to the current version 16.1 (v16) model, which utilized single DLG parameter. Dose calculations were performed and compared for (1) static small on-axis fields, (2) static small off-axis fields, (3) single-isocenter single-target (SIST) HyperArc plans, and (4) single-isocenter multiple-target (SIMT) HyperArc plans. Gafchromic EBT4 film and myQA SRS device were used for dose verification.

The measurement required for ELM was similar to that of the original DLG, but ELM configuration provided significant time savings. The measurements showed comparable or improved accuracy with the ELM model for both static fields and patient-specific plans. A significant improvement in dose calculation accuracy was observed with the ELM particularly for SIMT patients with a large number of small targets.

The new ELM introduced in Eclipse v18 substantially improves efficiency and consistency of the modeling process in the Eclipse dose calculation algorithm while maintaining comparable or superior accuracy for Linac-based SRS.