Gel for 3D Dosimetry by Optical Tomographic Densitometry

This project aims to develop a novel, tissue-equivalent gel-dosimeter of ionizing radiation, whichis capable of producing highly-resolved and accurate data on three dimensional dose distributions usingoptical tomographic densitometry. The dose-response mechanism relies on the production of Rayleighscattering micro-particles in the gel at the site of radiation absorption, where acrylic commonersdispersed in the gel are polymerized. Absorption and scattering of collimated light passing through theoptically turbid medium produces a net attenuation of light intensity that can be measured and is directlyrelated to the dose. Measurements of the projections of the optical density into different directions canbe used to reconstruct the distribution of radiation doses within the gel. Doses of the order of 10 Gycan be measured with a spatial resolution <1mm. In previous work, the MRI properties of the gel havebeen investigated and used very successfully to create 3D dose maps, but there are significantadvantages to the use of a simpler optical method of reading the dose distribution stored by the gel.The gel will find widespread use in radiation therapy practice, for 3D measurements in homogeneous andanthropomorphic phantoms, confirmation of computerized treatment planning and in quality assuranceprocedures. The goals of Phase I are to devise and evaluate a protocol for convenient and inexpensivepreparation of a prototype polymer-gel dosimeter optimized for optical densitometry, to demonstrate itsstability and reproducibility as well as spatial uniformity of the dose-response, and to evaluate thefeasibility of constructing a low-cost bench top optical scanner for the reconstruction of 3D dosedistributions.