# A multi‐institution performance assessment of a double‐layer MLC

## TL;DR

This study evaluates the performance of a new double-layer MLC used in Varian Halcyon and Ethos linacs across multiple institutions.

## Contribution

The study establishes typical performance ranges for the MLC and identifies a specific calibration issue.

## Key findings

- MLC performance indices are consistent with other linacs except for proximal layer calibration.
- Automated image analysis enabled reproducible performance assessment across 16 linacs.
- Typical ranges for Halcyon/Ethos MLC performance were successfully established.

## Abstract

Varian Halcyon and Ethos linacs use a novel double‐layer MLC.

To perform a multi‐institutional characterization of MLC performance of Varian Halcyon and Ethos linacs and establish the range of typical performance indices.

The tests used plans delivered to the megavoltage (MV) imaging panel that can be easily implemented and reproducibly delivered in different centers. Automated image analysis was used to obtain metrics that characterize the MLC performance. The tests included picket fence, MLC leakage, sweeping gap, open field symmetry changes, change of output with gantry angle, and volumetric modulated arc therapy (VMAT) indices. Sixteen linacs from 11 centers were included in the study.

Performance indices were found that are in line with other linacs, with the exception of proximal layer positional calibration.

Typical ranges have been established for Halcyon/Ethos MLC performance indices.