Three-dimensional dose verification for intensity modulated radiation therapy using optical CT based polymer gel...

Area of Science:

• Medical Physics
• Radiotherapy Dosimetry
• Image Reconstruction

Background:

• Intensity-modulated-radiation-therapy (IMRT) requires precise dose verification due to high dose gradients.
• Accurate 3D dose determination with high spatial resolution is crucial for IMRT.
• Existing dosimetry methods may have limitations in capturing complex 3D dose distributions.

Purpose of the Study:

• To implement and evaluate polymer gel dosimetry with optical CT scanning for 3D dose verification in IMRT.
• To assess the accuracy and spatial resolution of this dosimetry technique.
• To compare gel dosimetry measurements with treatment planning system calculations and film/ion chamber measurements.

Main Methods:

• Utilized BANG3 polymer gels in a cylindrical phantom for IMRT irradiation.
• Employed an optical CT scanner with a He-Ne laser for 3D dose reconstruction.
• Reconstructed dose distributions using filtered back-projection.
• Performed comparative dosimetry using solid water phantoms, EDR2 film, and ion chambers.
• Analyzed dose distributions using root mean square (rms) deviations for dose difference and distance-to-agreement (DTA).

Main Results:

• Isodose lines from gel dosimetry showed good agreement with treatment planning and film measurements on selected planes.
• Absolute point-dose measurements with ion chambers agreed within 4.2% of calculated doses.
• Comparison between gel measurements and treatment planning showed rms deviations of 2%-6% for dose difference and 1-3 mm for DTA.
• Optical CT-based polymer gel dosimetry demonstrated high spatial resolution and accuracy.

Conclusions:

• Optical CT-based polymer gel dosimetry is a viable method for high-resolution, 3D dose verification in IMRT.
• This technique can accurately assess dose distributions, particularly in critical areas with steep dose gradients.
• The findings support the potential of polymer gel dosimetry as a valuable tool in radiotherapy quality assurance.