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An EPID-based system for gantry-resolved MLC quality assurance for VMAT

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posted on 2025-05-10, 12:15 authored by Benjamin J. Zwan, Michael P. Barnes, Todsaporn Fuangrod, Cameron J. Stanton, Daryl O'ConnorDaryl O'Connor, Paul J. Keall, Peter B. Greer
Multileaf collimator (MLC) positions should be precisely and independently measured as a function of gantry angle as part of a comprehensive quality assurance (QA) program for volumetric-modulated arc therapy (VMAT). It is also ideal that such a QA program has the ability to relate MLC positional accuracy to patient-specific dosimetry in order to determine the clinical significance of any detected MLC errors. In this work we propose a method to verify individual MLC trajectories during VMAT deliveries for use as a routine linear accelerator QA tool. We also extend this method to reconstruct the 3D patient dose in the treatment planning system based on the measured MLC trajectories and the original DICOM plan file. The method relies on extracting MLC positions from EPID images acquired at 8.41fps during clinical VMAT deliveries. A gantry angle is automatically tagged to each image in order to obtain the MLC trajectories as a function of gantry angle. This analysis was performed for six clinical VMAT plans acquired at monthly intervals for three months. The measured trajectories for each delivery were compared to the MLC positions from the DICOM plan file. The maximum mean error detected was 0.07 mm and a maximum root-mean-square error was 0.8 mm for any leaf of any delivery. The sensitivity of this system was characterized by introducing random and systematic MLC errors into the test plans. It was demonstrated that the system is capable of detecting random and systematic errors on the range of 1-2mm and single leaf calibration errors of 0.5 mm. The methodology developed in the work has potential to be used for efficient routine linear accelerator MLC QA and pretreatment patient-specific QA and has the ability to relate measured MLC positional errors to 3D dosimetric errors within a patient volume.

History

Journal title

Journal of Applied Clinical Medical Physics

Volume

17

Issue

5

Pagination

348-365

Publisher

American College of Medical Physics

Language

  • en, English

College/Research Centre

Faculty of Science

School

School of Mathematical and Physical Sciences

Rights statement

This work is licensed under a Creative Commons Attribution 3.0 Unported License.

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