MRIgRT dynamic lung motion thorax anthropomorphic QA phantom: Design, development, reproducibility, and feasibility...

Area of Science:

• Medical Physics
• Radiotherapy
• Medical Imaging

Background:

• Credentialing Magnetic Resonance image-guided Radiotherapy (MRIgRT) systems is crucial for NCI-sponsored clinical trials.
• A validated, dynamic, anthropomorphic phantom is needed to simulate lung cancer patients for accurate system assessment.

Purpose of the Study:

• To design, manufacture, and evaluate a dynamic MRI/CT-compatible anthropomorphic thorax phantom.
• To serve as a credentialing tool for MRIgRT systems participating in NCI clinical trials.

Main Methods:

• Constructed a water-fillable acrylic thorax phantom with MR/CT-visible inserts simulating lung and tumor.
• Incorporated a pneumatic system for inhale/exhale motion simulation.
• Evaluated dose accuracy using TLDs and radiochromic film, with reproducibility and feasibility studies on Elekta Unity and MRIdian systems.

Main Results:

• Achieved reproducible TLD dose measurements (SD < 1.5%) on the Unity system.
• Gamma analysis passing rates of 93.3% (reproducibility) and 96.8% (feasibility) with 7%/5 mm criteria.
• Dose measurements were within acceptable criteria for all treatment evaluations across different MRIgRT systems.

Conclusions:

• Successfully constructed a dosimetrically tissue-equivalent, CT/MR visible, motion-enabled anthropomorphic thorax phantom.
• The phantom is a validated and appropriate NIH credentialing tool for MRIgRT systems.
• This tool supports accurate treatment delivery and patient safety in lung cancer radiotherapy trials.