Small field dose delivery evaluations using cone beam optical computed tomography-based polymer gel dosimetry

Area of Science:

• Medical Physics
• Radiotherapy Dosimetry
• Polymer Gel Dosimetry

Background:

• Accurate three-dimensional (3D) dose imaging is crucial for small field radiation therapy.
• Cone beam optical computed tomography (CBCT) offers potential for 3D dosimetry but is susceptible to scattered light.
• N-isopropylacrylamide (NIPAM)-based polymer gels are used as dosimeters but require precise imaging techniques.

Purpose of the Study:

• To evaluate the combination of CBCT with NIPAM polymer gel dosimeters for 3D dose imaging.
• To investigate the impact of scattered stray light on optical CT dosimetry accuracy.
• To improve NIPAM gel dosimetry performance through optimized preparation methods.

Main Methods:

• Utilized cone beam optical computed tomography (CBCT) for imaging NIPAM polymer gel dosimeters.
• Compared optical CT dose readout with magnetic resonance imaging (MRI) for initial dosimetry assessment.
• Modified NIPAM gel preparation techniques to mitigate scattered light and enhance imaging compatibility.

Main Results:

• Initial optical CT dose readout showed significant failures (60% pass rate at 3%/3mm) compared to MRI (93% pass rate).
• Modified NIPAM gel preparation improved optical CT performance to 99.7% pass rate at 3%/3mm and 92.7% at 2%/2mm.
• Modified dosimeters exhibited good inter- and intrabatch agreement (within 3.8%) for dose response calibration.

Conclusions:

• Optimized NIPAM gel preparation is essential for accurate CBCT-based 3D dosimetry.
• The improved method significantly enhances the reliability of optical CT for small field radiation dosimetry.
• Modified NIPAM gels show potential for dose sensitivity calibration in radiotherapy applications.