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MRIgRT head and neck anthropomorphic QA phantom: Design, development, reproducibility, and feasibility study.
A Steinmann1, P Alvarez1, H Lee1
1Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX, 77030, USA.
Medical Physics
|December 7, 2019
Summary
A new head and neck phantom for MRI-guided radiotherapy (MRIgRT) ensures quality assurance in clinical trials. This tissue-equivalent phantom is visible on both MR and CT, proving useful for NCI-sponsored studies.
Area of Science:
- Medical Physics
- Radiotherapy Technology
- Medical Imaging
Background:
- Magnetic Resonance Imaging-guided Radiotherapy (MRIgRT) requires robust quality assurance (QA) tools.
- Existing QA methods may not adequately assess the end-to-end performance of MRIgRT systems.
Purpose of the Study:
- To design, manufacture, and evaluate a novel anthropomorphic head and neck (H&N) phantom.
- This phantom is designed for dual MR/CT visibility and serves as an end-to-end QA tool for MRIgRT systems in NCI-sponsored clinical trials.
Main Methods:
- Constructed a water-fillable acrylic H&N phantom with inserts mimicking organs at risk and planning target volumes using synthetic gel and Superflab.
- Employed radiochromic film and thermoluminescent detectors (TLDs) for dose measurement.
- Conducted end-to-end testing including imaging, treatment planning, MR verification, and irradiation on Elekta Unity and ViewRay MRIdian systems.
Main Results:
- Reproducible TLD doses (SD < 1.5%) were achieved on the Unity system, with measured TLD to calculated dose ratios between 0.94-0.98.
- Gamma analysis (7%/4 mm) showed high passing rates for both ViewRay (96.2-97.3%) and Unity (89.7-97.8%) systems.
- All results met IROC-Houston credentialing criteria for TLDs and gamma analysis.
Conclusions:
- Successfully developed a tissue-equivalent, MR/CT-visible H&N phantom for MRIgRT.
- Initial testing indicates the phantom's potential as a valuable credentialing tool for NCI-clinical trials utilizing MRIgRT systems.
