Detection of the Linac Jaw Face Angle Misalignment Using High Energy Electron Beam Symmetry

Authors

Song Gao
Andres Cibrian
Jared Ohrt
Peter Balter

Language

English

Publication Date

12-26-2025

Journal

Journal of Applied Clinical Medical Physics

DOI

10.1002/acm2.70419

PMID

41373064

PMCID

PMC12695474

PubMedCentral® Posted Date

12-10-2025

PubMedCentral® Full Text Version

Post-print

Abstract

Purpose: To demonstrate the usage of a high energy electron beam symmetry measured at different collimator angles to detect jaws face angle misalignments on Varian TrueBeam linear accelerators (linac) during acceptance and commissioning processes.

Methods: During the linac acceptance, all beams were steered to a symmetric shape with the gantry and collimator at 0°. We noted that the symmetries of higher energies electrons (e.g., 16 MeV, 20 MeV) changed over 2% when measured with the collimator at 90° and/or 270° for two linacs commissioned within 5-months of each other. Misaligned applicators were ruled out as the cause of this issue. Eventually, this was traced to the X-jaw face angle not matching beam divergence. After the problem was identified and the jaws were realigned by manufacture's engineers and all beams were re-steered to a symmetric shape at collimator 0° and verified at collimator 90° and 270°.

Results: Prior to the manufacturer adjusting the jaw face angles, the maximum observed electron beam symmetry changes with 90° collimator rotation were 2.0% and 2.6% for linac 1 and linac 2, respectively. After realigning, the jaw face angles the maximum observed electron beam symmetry changes with 90° collimator rotation were within 1.0% for all beams on both linacs.

Conclusion: We have demonstrated that changes in symmetry of high energy electron beam with 90° collimator rotation can signal that the jaw face angle is not properly aligned with beam divergence.

Keywords

Particle Accelerators, Humans, Electrons, Radiotherapy Dosage, Radiotherapy Planning, Computer-Assisted, Phantoms, Imaging, Radiotherapy, Intensity-Modulated, Radiotherapy Setup Errors, acceptance and commissioning, beam symmetry, jaw face angle, linear accelerator

Published Open-Access

yes

Recommended Citation

Gao, Song; Cibrian, Andres; Ohrt, Jared; et al., "Detection of the Linac Jaw Face Angle Misalignment Using High Energy Electron Beam Symmetry" (2025). Faculty, Staff and Student Publications. 5332.
https://digitalcommons.library.tmc.edu/uthgsbs_docs/5332