Evaluation of three-dimensional polymer gel dosimetry using X-ray CT and R2 MRI

Area of Science:

• Medical Physics
• Radiological Imaging
• Radiation Dosimetry

Background:

• Traditional polymer gel dosimetry using spin-spin relaxation (R2) magnetic resonance imaging (MRI) faces challenges in acquiring thin slice images.
• This limitation hinders detailed three-dimensional (3D) dose reconstruction, particularly for proton beam therapy.

Purpose of the Study:

• To investigate the feasibility of using X-ray computed tomography (CT) for thin slice dose reading in polymer gel dosimetry.
• To compare the image quality and precision of CT-based dosimetry with conventional R2 MRI methods.

Main Methods:

• Proton beam dose distributions were measured using polymer gels.
• Dose reading was performed using X-ray computed tomography (CT) to acquire thin slices.
• Three-dimensional (3D) images were reconstructed using volume rendering.
• Image quality metrics, including signal-to-noise ratio and coefficient of variation, were analyzed.

Main Results:

• X-ray CT enabled the acquisition of significantly thinner slices compared to R2 MRI, yielding more detailed 3D dose data with smaller voxel sizes.
• A decrease in signal-to-noise ratio was observed with thinner slices and smaller voxels.
• The coefficient of variation for non-irradiated gels was lower with CT than with R2 MRI, indicating higher precision.

Conclusions:

• X-ray CT is a viable alternative for thin slice dose reading in polymer gel dosimetry, offering enhanced 3D data resolution.
• While signal-to-noise ratio needs consideration, CT provides superior precision over R2 MRI for dose measurements.