An improved abdominal phantom for intrafraction image guidance validation.

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Medical Imaging

Background:

• Simulating organ motion in radiotherapy is crucial for accurate treatment delivery.
• Existing phantoms often lack anatomical realism and precise motion simulation capabilities.
• Developing advanced phantoms aids in testing novel radiotherapy techniques like image-gated beam delivery.

Purpose of the Study:

• To develop a dynamically compressible abdominal phantom that simulates breathing-induced organ motion.
• To create a phantom compatible with Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) for dosimetric data acquisition.
• To enhance anatomical realism and ultrasound imaging compatibility for improved radiotherapy testing.

Main Methods:

• Constructed a polyvinyl chloride plastisol (PVCP) phantom with a cavity for a deformable normoxic polyacrylamide gel (nPAG) dosimeter.
• Utilized 3D-printed molds from patient CT data to create anatomically realistic component organs with adjustable radiodensities.
• Incorporated graphite scatterers for ultrasound compatibility and assessed motion repeatability using CT with fiducial markers and iodinated gelatin inserts.

Main Results:

• The phantom components exhibit CT values similar to human tissues, enhancing anatomical realism.
• Maximum motion of a phantom fiducial was 12.2 mm, simulating realistic organ movement during breathing.
• Achieved high dosimeter motion repeatability (within 0.3 mm on average) and contour repeatability (Dice coefficients > 0.98).

Conclusions:

• The developed abdominal phantom accurately simulates organ motion for radiotherapy applications.
• The phantom's design supports MRI and ultrasound imaging, providing valuable dosimetric and motion tracking data.
• This advanced phantom is a promising tool for testing image-gated beam delivery and improving radiotherapy precision.