Distribution of the dose response in a silicone-based radio-fluorogenic dosimeter and FWT-60 irradiated with monochromatic low-energy X-rays

Abstract

In a previous work, we studied the electron spin resonance imaging of the alanine dosimeter irradiated with 0.36–1.8 kGy of 4- and 7-keV monochromatic X-rays and visualized the distribution of alanine radicals as a function of the penetration depth of the X-rays. Herein, the dose-response profile, as a function of the penetration depth, of a silicone-based gel dosimeter and FWT-60 film dosimeter was studied for comparison with the alanine dosimeter. A silicone-based gel dosimeter using dihydrorhodamine 6G (DHR6G) as a fluorescence probe was irradiated with 0–45 Gy of 10-keV monochromatic X-rays. The dose-response profile of the fluorescence was then investigated in detail to demonstrate the properties of low-energy X-ray irradiation. The fluorescence intensity at the surface was less than that inside when irradiated with a higher dose. The total fluorescence intensity per unit dose decreased with the increasing dose. These results were almost the same as those for the alanine dosimeter. At the surface, many of the radicals produced in the silicone elastomer would be lost due to radical-radical recombination before reacting with DHR6G owing to the high linear energy transfer nature of the low-energy X-ray irradiation. The FWT-60 film dosimeter was irradiated with 0.8–10 kGy of 2- and 4-keV monochromatic X-rays. For the FWT-60 film, the dose-response linearly increased with the dose, although its efficiency was far lower than that of the gel dosimeter. Additionally, the slope of the dose-response decreased with the decreasing photon energy. Some of the precursor molecules for the pigment will be directly ionized, transforming into the coloring agent in the FWT-60 film. Finally, the reaction mechanism to produce the pigment in each dosimeter would affect the dose-response properties of irradiation via low-energy X-rays.