Characterization of a new radiochromic three-dimensional dosimeter

The development of intensity-modulated radiotherapy (IMRT) has created a clear need for a dosimeter that can accurately and conveniently measure dose distributions in three dimensions to assure treatment quality. PRESAGE (TM) is a new three dimensional (3D) dosimetry material consisting of an optically clear polyurethane matrix, containing a leuco dye that exhibits a radiochromic response when exposed to ionizing radiation. A number of potential advantages accrue over other gel dosimeters, including insensitivity to oxygen, radiation induced light absorption contrast rather than scattering contrast, and a solid texture amenable to machining to a variety of shapes and sizes without the requirement of an external container. In this paper, we introduce an efficient method to investigate the basic properties of a 3D dosimetry material that exhibits an optical dose response. The method is applied here to study the key aspects of the optical dose response of PRESAGE (TM): linearity, dose rate dependency, reproducibility, stability, spectral changes in absorption, and temperature effects. PRESAGE (TM) was prepared in 1 X 1 X 4.5 cm(3) optical cuvettes for convenience and was irradiated by both photon and electron beams to different doses, dose rates, and energies. Longer PRESAGE (TM) columns (2 X 2 X 13 cm(3)) were formed without an external container, for measurements of photon and high energy electron depth-dose curves. A linear optical scanning technique was used to detect the depth distribution of radiation induced optical density (OD) change along the PRESAGE (TM) columns and cuvettes. Measured depth-OD curves were compared with percent depth dose (PDD). Results indicate that PRESAGE (TM) has a linear optical response to radiation dose (with a root mean square error of similar to 1%), little dependency on dose rate (similar to 2%), high intrabatch reproducibility (< 2%), and can be stable (similar to 2%) during 2 hours to 2 days post irradiation. Accurate PRESAGE (TM) dosimetry requires temperature control within 1 degrees C. Variations in the PRESAGE (TM) formulation yield corresponding variations in sensitivity, stability, and density. CT numbers in the range 100-470 were observed. In conclusion, the small volume studies presented here indicate PRESAGE (TM) to be a promising, versatile, and practical new dosimetry material with applicability for radiation therapy. (c) 2006 American Association of Physicists in Medicine.