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 × 1 × 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 × 2 × 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 ∼ 1 % ), little dependency on dose rate ( ∼ 2 % ) , high intrabatch reproducibility ( < 2 % ) , and can be stable ( ∼ 2 % ) during 2 hours to 2 days post irradiation. Accurate PRESAGE TM dosimetry requires temperature control within 1 ° 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.