SU-E-J-164: An Investigation of a Low-Cost 'dry' Optical-CT Scanning System for 3D Dosimetry.

PURPOSE To characterize and explore the efficacy of a novel low-cost, lowfluid, broad-beam optical-CT system for 3D-dosimetry in radiochromic Presage dosimeters. Leading current optical-CT systems incorporate expensive glass-based telecentric lens technology, and a fluid bath with substantial amounts of fluid (which introduces an inconvenience factor) to minimize refraction artifacts. Here we introduce a novel system which addresses both these limitations by: (1) the use of Fresnel lenses in a telecentric arrangement, and (2) a 'solid' fluid bath which dramatically reduces the amount of fluid required for refractive-index (RI) matching. Materials METHODS: A fresnel based telecentric optical-CT system was constructed which expands light from a single red LED source into a nominally parallel beam into which a cubic 'dry-tank' is placed. The drytank consists of a solid polyurethane cube (with the same RI as Presage) but containing a cylindrical cavity (11.5cm diameter × 11cm) into which the dosimeter is placed for imaging. A narrow (1-3mm) gap between the walls of the dosimeter and dry-tank is filled with a fluid of similar RI. This arrangement reduces the amount of RI fluid from about 1000cc to 75cc, yielding substantial practical benefit in convenience and cost. The new system was evaluated in direct comparison against Eclipse planning system from a 4-field parallel-opposed treatmen RESULTS: Gamma calculations of dose from DFOS-dry system versus Eclipse showed 92% and 97% agreement with 4mm/4% and 5mm/5% criteria, respectively, in the central 80% of dose distribution. Reconstructions showed some edge artifacts, as well as some dose underestimation towards the dosimeter edge. CONCLUSION The implementation of Fresnel based 'dry' optical-CT for 3Ddosimetry would represent an important advance enhancing costeffectiveness and practical viability. The performance of the prototype presented here is not yet comparable to the state-of-the-art, but shows sufficient promise for further investigation to elevate image quality to match gold-standard optical-CT systems. This work was supported by NIH R01CA100835.