Robust enhanced leaf model implementation for beam-matched linear accelerators: Impact of physical leaf gap variations.
- 1Department of Radiation Oncology, NYU Langone Health, New York, New York, USA.
- 2Department of Radiation Oncology, Boston Medical Center, One Boston Medical Center Place, Boston University Chobanian & Avedisian School of Medicine, Boston, Massachusetts, USA.
Abstract
Background
Leaf-gap variability may influence MLC modeling when implementing the Enhanced Leaf Model (ELM) in Eclipse v18.0 for beam-matched linear accelerators (linacs) previously commissioned using legacy dosimetric leaf gap (DLG)-based models.Purpose
To characterize inter-machine variability in calibrated leaf gaps and associated ELM-derived MLC parameters across beam-matched linacs and to develop a practical strategy for robust multi-linac ELM implementation.Methods
Five TrueBeam linacs equipped with Millennium 120 MLC were grouped into two clinical sites (Group A: three linacs; Group B: two linacs) sharing a matched beam model within each group. Variations in calibrated leaf-gap, measured DLG, and DLG (ELM) values were evaluated. Leaf-gap variation was harmonized by adjusting Gap value in the machine setting while maintaining a machine-averaged ELM across beam-matched linacs. ELM performance was evaluated using three MLC test plans: dynamic MLC (dMLC), narrow MLC (nMLC), and static MLC (sMLC). Following Gap adjustment, DLG was remeasured, and DLG (ELM) values were verified. Central doses of dMLC fields were measured using an ionization chamber and compared with ELM-calculated doses. Dose profiles were measured with radiochromic film, and were compared with calculated profiles before and after Gap adjustment. Profile agreement was further quantified using full width at half maximum (FWHM) and one-dimensional gamma analysis (2%/1 mm, 10% dose threshold).Results
In Group A, ELM-derived MLC parameters showed minimal variation, with DLG (ELM) values agreeing within 0.02 cm among the linacs with Gap values set to zero for all linacs. Film measurements demonstrated excellent agreement between calculated and measured dose distributions for all MLC test fields, with nMLC gamma passing rates generally exceeding 98% and FWHM differences within 0.2 mm. In Group B, an initial 0.05 cm difference in Gap value resulted in substantial discrepancies in dMLC tests, including central dose deviations of -7.5% and +5.0% relative to the corresponding calculated doses and approximately 0.05 cm difference in the measured dMLC field width. Following Gap adjustment, ELM-derived parameters were converged and dosimetric agreement was improved markedly, with dMLC central dose differences reduced to within ± 1.1%. nMLC tests resulted in gamma pass rates exceeding 98%, and FWHM differences within 0.2 mm across all positions.Conclusions
The calibrated leaf-gap, represented by the Gap value in the machine setting, directly influences DLG (ELM), measured DLG and dMLC dose response. Dynamic sweeping-gap measurements provide a sensitive and efficient method for validating ELM performance and identifying residual inter-machine discrepancies. A hybrid strategy combining machine-averaged ELM parameters with harmonized leaf-gap settings provides a practical and robust approach for multi-linac ELM implementation.
Related
- Commissioning of Medical Linear Accelerators in India: A Survey of Regulatory Compliance, Clinical Implementation, and Professional Challenges
- OptiLookUp: A Microring-Based Photonic Read-Only Memory Lookup Table Engine for Photonic Accelerators
- Controlling external injection in laser-plasma accelerators with terahertz frequency bunch manipulation
- RF Power Transport for Accelerators
- Wakefield-Dressed Relativistic Vortex Electrons in Plasma Accelerators
BibTeX
@article{lee2026robust,
title = {{Robust enhanced leaf model implementation for beam-matched linear accelerators: Impact of physical leaf gap variations.}},
author = {Soyoung Lee and Paulina E Galavis and Siyoung Jang},
journal = {Journal of applied clinical medical physics},
year = {2026},
month = oct,
doi = {10.1002/acm2.70895},
url = {https://europepmc.org/article/MED/42961336},
note = {CC BY},
}
RIS
TY - JOUR
TI - Robust enhanced leaf model implementation for beam-matched linear accelerators: Impact of physical leaf gap variations.
AU - Soyoung Lee
AU - Paulina E Galavis
AU - Siyoung Jang
PY - 2026
DA - 2026/10/30
JO - Journal of applied clinical medical physics
DO - 10.1002/acm2.70895
UR - https://europepmc.org/article/MED/42961336
AB - Background Leaf-gap variability may influence MLC modeling when implementing the Enhanced Leaf Model (ELM) in Eclipse v18.0 for beam-matched linear accelerators (linacs) previously commissioned using legacy dosimetric leaf gap (DLG)-based models.Purpose To characterize inter-machine variability in calibrated leaf gaps and associated ELM-derived MLC parameters across beam-matched linacs and to develop a practical strategy for robust multi-linac ELM implementation.Methods Five TrueBeam linacs equipped with Millennium 120 MLC were grouped into two clinical sites (Group A: three linacs; Group B: two linacs) sharing a matched beam model within each group. Variations in calibrated leaf-gap, measured DLG, and DLG (ELM) values were evaluated. Leaf-gap variation was harmonized by adjusting Gap value in the machine setting while maintaining a machine-averaged ELM across beam-matched linacs. ELM performance was evaluated using three MLC test plans: dynamic MLC (dMLC), narrow MLC (nMLC), and static MLC (sMLC). Following Gap adjustment, DLG was remeasured, and DLG (ELM) values were verified. Central doses of dMLC fields were measured using an ionization chamber and compared with ELM-calculated doses. Dose profiles were measured with radiochromic film, and were compared with calculated profiles before and after Gap adjustment. Profile agreement was further quantified using full width at half maximum (FWHM) and one-dimensional gamma analysis (2%/1 mm, 10% dose threshold).Results In Group A, ELM-derived MLC parameters showed minimal variation, with DLG (ELM) values agreeing within 0.02 cm among the linacs with Gap values set to zero for all linacs. Film measurements demonstrated excellent agreement between calculated and measured dose distributions for all MLC test fields, with nMLC gamma passing rates generally exceeding 98% and FWHM differences within 0.2 mm. In Group B, an initial 0.05 cm difference in Gap value resulted in substantial discrepancies in dMLC tests, including central dose deviations of -7.5% and +5.0% relative to the corresponding calculated doses and approximately 0.05 cm difference in the measured dMLC field width. Following Gap adjustment, ELM-derived parameters were converged and dosimetric agreement was improved markedly, with dMLC central dose differences reduced to within ± 1.1%. nMLC tests resulted in gamma pass rates exceeding 98%, and FWHM differences within 0.2 mm across all positions.Conclusions The calibrated leaf-gap, represented by the Gap value in the machine setting, directly influences DLG (ELM), measured DLG and dMLC dose response. Dynamic sweeping-gap measurements provide a sensitive and efficient method for validating ELM performance and identifying residual inter-machine discrepancies. A hybrid strategy combining machine-averaged ELM parameters with harmonized leaf-gap settings provides a practical and robust approach for multi-linac ELM implementation.
SN - 1526-9914
ER -