DOI
https://doi.org/10.25772/BNFT-9T98
Author ORCID Identifier
0000-0003-0627-8903
Defense Date
2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Medical Physics
First Advisor
William Song
Second Advisor
Siyong Kim
Third Advisor
Tianjun Ma
Fourth Advisor
Frank Corwin
Abstract
The 0.35 T MR-Linac combines MRI and linear-accelerator technology to enable organ-motion gating, adaptive radiotherapy, and radiobiological optimization through diffusion-weighted imaging (DWI). Operating at 0.35 T, it delivers a single-energy 6 MV flattening-filter-free (FFF) photon beam. Comprehensive quality assurance (QA) therefore covers both imaging and accelerator components. Acceptance testing protocols were evaluated to establish baselines for routine QA and to identify system limitations. Novel analysis methods quantified the magnetic-field effect on 6 MV FFF beam-scanning profiles. Large, medium, and small fields were characterized with twelve MR-compatible detectors—plastic scintillators, diodes, diamond detectors, and ionization chambers—spanning diverse shapes and sensitive volumes. A renormalization approach defined penumbra-region profile shapes for large fields, while quantifiable parameters captured the pronounced shifts in small-field profiles caused by the 0.35 T field. To meet small-field dosimetry requirements, field-output factors were measured with sixteen detectors (including Gafchromic film) and detector-specific correction factors from the smallest to the reference field were derived. Cherenkov corrections for plastic scintillators were refined through a novel multi-loop method. Dose- and latency-gating performance was evaluated with a plastic scintillator in a motion-gating phantom; synchronized linac, phantom, and detector signals yielded gating latency and dose-delivery accuracy across three gantry angles, all tracking algorithms, and slow, medium, and fast motion patterns. MRI commissioning was streamlined by optimizing 2-D T1 and T2 scan protocols on a large-FOV phantom, reducing acquisition time while maintaining image quality. Finally, clinical comparisons of four commercial phantoms imaged with the TRUFI sequence assessed distortion versus gantry angle and image-quality parameters according to each phantom’s specifications.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
8-5-2025