AbstractID: 8240 Title: Accuracy of a High-Resolution Optical CT Scanning System for
Polymer Gel Dosimetry as Applied to Intravascular Brachytherapy
It is well established that the steep dose gradients employed in intravascular brachytherapy
require that doses be measured with 100 micron resolution. One dosimetry system potentially
suitable for this application is polymer-gel dosimetry using high-resolution laser CT scanning.
This method is based on radiation-induced polymerization that leads to the formation of submicron micro-particles in the gel. Optical attenuation in the gel, caused by light scattering on
polymer particles, is proportional to the radiation dose. In this study we used a prototype scanner
that is currently under development at MGS Research, Inc. (Madison, CT). The scanner utilizes
the cylindrical geometry of the gel sample to collect the transmitted light at a single
photodetector site that remains stationary during the scan. In order to compress the laser beam
down to 100 micron diameter over a 3cm field of view inside the gel, a beam expander together
with beam-focusing optics are used. This paper reports the result of analysis and design
improvements related to the dosimetric accuracy of the scanner-gel system. The dose (or
percentage dose) is calibrated to density per unit length, that is derived from reconstructed
optical CT images. The sources of dosimetric uncertainty can be both in the gel and in the
scanner. In this study we focus on the instrument-generated errors and on the possible extent of
their reduction. Factors that can affect the signal-to-noise ratio include the dynamic range and
bandwidth of the detector, A/D resolution, and signal post-processing. This work is supported by
NIH grant 2R44 HL059813.