SU‐FF‐I‐153: First Experience of High Resolution 3D Optical‐CT Scanning of An Anthropomorphic, Leuco‐Dye Doped, Radiochromic Plastic Dosimeter

Abstract

Purpose: To investigate feasibility of high‐resolution three dimensional (3D) optical‐CT scanning of an anthropomorphic leuco‐dye doped radiochromic plastic dosimeter. Method and Materials: An anthropomorphic head phantom made out of PRESAGE™ (a leuco‐dye‐doped radiochromic plastic) was from Heuris Pharma. Co‐planar alignment marks (visible on x‐ray CT and optical‐CT) were placed on the surface. These were used to setup the phantom for x‐ray CT and treatment and for registration of measured dose from optical‐CT with the eclipse treatment planning system calculations. A RapidArc™ treatment for brain tumor was delivered and radiochromic response was scanned using optical‐CT. Optical‐CT (pre‐irradiation and post‐irradiation) was with a commercial laser beam scanner called OCTOPUS‐5X™ (MGS Research Inc). The following imaging parameters were used: Image matrix of 418×418, pixel size of 0.5 mm, 1200 projections at 0.3 degree angular increments and inter‐slice spacing of 2.5 mm. The relationship between post‐irradiation radiochromic response and dose was established by irradiation of 1 cm path‐length cuvettes to a known dose and measuring the corresponding optical density change. Results: Pre‐irradiation and post‐irradiation optical‐CT scans of the head‐phantom were promising with artefacts generally confined to the edge because of refractive index mismatch between scanning fluid and phantom material. Even with a refractive index mismatch, challenging surfaces like the nose and ears were reconstructed with clarity. A profile through the center of the reconstructed central slice was flat suggesting uniform optical density. Further improvements to optical‐CT images are possible by satisfying the Nyquist sampling‐sufficiency criteria and with precise refractive index matching. Cuvette irradiations confirmed that the relationship between delivered dose and radiochromic response was linear with a slope of 0.0144 OD change per Gray. Conclusion: Results suggest that anthropomorphic dosimetry phantoms could be used for patient specific 3D quality‐assurance in the near future, which represents a major advance in the field of 3D dosimetry.