Cone beam optical computed tomography for gel dosimetry I: scanner characterization

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Image Reconstruction

Background:

• Gel dosimetry offers a promising method for radiation dose measurement in cancer treatment.
• Accessibility and speed of optical readout tools are critical for clinical adoption.
• Cone beam computed tomography (CT) offers potential for rapid 3D dose reconstruction.

Purpose of the Study:

• To characterize the performance of the Vista cone beam CCD-based optical scanner for gel dosimetry.
• To evaluate the suitability of filtered back projection cone beam reconstruction for optically absorbing dosimeters.
• To assess the system's accuracy, resolution, and precision for dose measurements.

Main Methods:

• Characterization of the Vista cone beam CCD scanner.
• Application of filtered back projection cone beam reconstruction algorithm.
• Imaging of a polyethylene terephthalate (PETE) jar dosimeter filled with optically absorbing media.
• Analysis of spatial distortion, measurement accuracy, signal-to-noise ratio, and inter-day precision.
• Investigation of stray light effects on absorption and scattering dosimeters.

Main Results:

• The Vista scanner achieved high-resolution (0.5 x 0.5 x 0.5 mm(3)) imaging in under 20 minutes.
• Measurement accuracy was 3-4% with a signal-to-noise ratio >100 for specific absorption ranges.
• Inter-day scan precision of 1% was achieved.
• Stray light caused artifacts in absorption measurements, limiting accuracy.
• Scattering dosimeters showed nonlinear effects and significant cupping artifacts due to scatter perturbation.

Conclusions:

• The Vista cone beam scanner shows potential for rapid, high-resolution gel dosimetry in clinical settings.
• Accuracy is limited by stray light artifacts, especially for scattering gel dosimeters.
• Further improvements in managing stray light are needed to enhance the reliability of optical readout for scattering media.