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Related Experiment Video

Updated: Jul 4, 2025

Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator

Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator

Published on: May 9, 2014

MV-based relative electron density estimation (iMREDe) for MR-LINAC dose calculation.

Marios Myronakis¹, Yue-Houng Hu¹, Matthew William Jacobson¹

¹Department of Radiation Oncology, Brigham and Women's Hospital, Dana Farber Cancer Institute and Harvard Medical School, Boston, Massachusetts, USA.

Medical Physics

|February 3, 2024

Summary

This summary is machine-generated.

This study developed a new method using a flat-panel imager and the primary MV beam to create accurate electron density maps for MR-LINAC systems. This advancement aids adaptive radiotherapy planning, improving efficiency and reducing uncertainties.

Keywords:

CBCT EPID MR-LINAC MV imaging electron density

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Last Updated: Jul 4, 2025

Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator

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Published on: May 9, 2014

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Area of Science:

Medical Physics
Radiotherapy Technology
Image Reconstruction

Background:

Magnetic Resonance Linear Accelerator (MR-LINAC) systems are vital for real-time adaptive radiotherapy.
Challenges with MR imaging of air cavities and electron density estimation hinder treatment planning efficiency and accuracy.
Current methods may introduce dose calculation uncertainties due to inaccurate electron density maps.

Purpose of the Study:

To demonstrate the generation of accurate electron density maps using the primary MV beam with a flat-panel imager.
To validate a novel technique for electron density map generation in MR-LINAC systems.
To improve the efficiency and accuracy of adaptive radiotherapy planning.

Main Methods:

Monte Carlo simulations of the ViewRay MRIdian MR-LINAC system, including magnetic field effects on a flat panel detector.
Simulated projection acquisition over 360 degrees for digital phantoms and a Head and Neck cancer patient.
Developed and applied artifact correction techniques (air normalization, in-painting) and generated electron density maps for comparison with CT-based maps.

Main Results:

The magnetic field significantly impacts the detector's point-spread function at field strengths above 50 mT.
Shim correction effectively removed reconstruction artifacts without compromising noise linearity.
The proposed method achieved an average relative difference of 11% in electron density maps compared to treatment planning CT.

Conclusions:

The iMREDe technique successfully generates accurate electron densities for the ViewRay MR-LINAC using a flat-panel imager and MV beam.
This method shows feasibility for improving adaptive radiotherapy workflows in MR-LINAC systems.
The findings represent a significant step towards reducing planning time and effort in adaptive radiotherapy.