Introduction of a deformable x-ray CT polymer gel dosimetry system

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Polymer Gel Dosimetry

Background:

• Accurate radiation dose measurement is crucial for radiotherapy.
• Existing dosimetry systems often lack the ability to accurately measure dose in deformable tissues.
• 3D polymer gel dosimetry offers high spatial resolution but typically requires rigid setups.

Purpose of the Study:

• To introduce and characterize the first 3D deformable dosimetry system using X-ray CT polymer gel.
• To evaluate the system's setup reproducibility, deformation capabilities, and dose response.
• To assess the dosimetric accuracy and spatial uniformity of the deformable system.

Main Methods:

• Utilized a N-isopropylacrylamide (NIPAM)-based polymer gel in a deformable latex balloon container.
• Incorporated wax beads as fiducial markers for tracking deformation and setup.
• Irradiated gels with known patterns to assess dose response and spatial uniformity.
• Analyzed CT images to determine setup reproducibility and deformation limits.
• Compared gel measurements with Monte Carlo dose calculations.

Main Results:

• Achieved excellent dosimetric accuracy (1.5% mean dose discrepancy) comparable to non-deformable systems.
• Demonstrated high setup reproducibility with sub-millimetre accuracy.
• The system successfully deformed up to 30 mm and recovered without damage, with reproducible internal deformations.
• Showed good spatial dose uniformity, with minor discrepancies at the container edge.

Conclusions:

• The developed 3D deformable dosimetry system is accurate, reproducible, and robust.
• It shows significant promise for validating deformable dose accumulation algorithms in radiotherapy.
• This system represents a valuable advancement for clinical applications requiring dose measurement in moving or deforming targets.