Scanning laser optical computed tomography system for large volume 3D dosimetry.

Area of Science:

• Medical Physics
• Optical Imaging
• Radiation Dosimetry

Background:

• Stray light in optical computed tomography (CT) introduces artifacts, compromising radiation dosimetry accuracy in gels and solids.
• Large dosimeter volumes, essential for verifying modern radiotherapy, amplify scatter effects, further challenging accurate measurements.

Purpose of the Study:

• To design and characterize an optical CT system capable of high-accuracy primary transmission measurements.
• To achieve effective stray light rejection while maintaining practical scan speeds for clinical applications.
• To enable accurate dosimetry for large volume dosimeters used in radiotherapy dose verification.

Main Methods:

• Developed an optical imaging platform utilizing a galvanometer mirror for horizontal scanning and a translation stage for vertical movement.
• Implemented a laser beam and small area detector to minimize stray light production and acceptance.
• Employed a custom lens-shaped optical CT aquarium for parallel ray sampling of projections.

Main Results:

• The scanner images 15 cm diameter, 12 cm height volumes at 0.33 mm resolution in approximately 30 minutes.
• Reconstructed attenuation coefficients agreed within 2% with independent cuvette measurements for various solutions and phantoms.
• Demonstrated excellent linearity for transmissions between 90% and 2%, indicating high measurement fidelity.

Conclusions:

• The developed optical CT system effectively rejects stray light, enhancing measurement accuracy.
• The system provides accurate dosimetry for large volume dosimeters within a clinically relevant timeframe.
• This technology holds promise for improving radiotherapy dose verification procedures.