Dose distributions have become more complex with the introduction of image-guided brachytherapy in high-dose-rate (HDR) brachytherapy treatments. Therefore, to correctly execute HDR, conducting a quality assurance programme for the remote after-loading system and verifying the dose distribution in the patient treatment plan are necessary. The characteristics of the dose distribution of HDR brachytherapy are that the dose is high near the source and rapidly drops when the distance from the source increases. Therefore, a measurement tool corresponding to the characteristic is required. In this study, using an Iridium-192 (Ir-192) source, we evaluated the basic characteristics of a nanoclay-based radio-fluorogenic gel (NC-RFG) dosimeter that is a fluorescent gel dosimeter using dihydrorhodamine 123 hydrochloride as a fluorescent probe. The two-dimensional dose distribution measurements were performed at multiple source positions to simulate a clinical plan. Fluorescence images of the irradiated NC-RFG were obtained at a high resolution (0.04 mm pixel–1) using a gel scanner with excitation at 465 nm. Good linearity was confirmed up to a dose range of 100 Gy without dose rate dependence. The dose distribution measurement at the five-point source position showed good agreement with the treatment planning system calculation. The pass ratio by gamma analysis was 92.1% with a 2%/1 mm criterion. The NC-RFG dosimeter demonstrates to have the potential of being a useful tool for quality assurance of the dose distribution delivered by HDR brachytherapy. Moreover, compared with conventional gel dosimeters such as polymer gel and Fricke gel dosimeters it solves the problems of diffusion, dose rate dependence and inhibition of oxygen-induced reactions. Furthermore, it facilitates dose data to be read in a short time after irradiation, which is useful for clinical use.
Dosimetry of spatial dose distribution of ionizing radiation in tissue equivalent materials using high sensitive radio-fluorogenic gel dosimeter using DHR123 with sensitizer. (Radiation therapy planning image courtesy of Varian Medical Systems, Inc. All rights reserved.)
Rhodamine 6G (R6G) and 7-diethylamino-4-methylcoumarin (7D4MC) were applied to a nanoclay gel dosimeter based on radiation-induced degradation. The radiological properties were evaluated under X-ray irradiation. The fluorescent dyes showed linear degradation with an increase in dose. In addition, the distribution of fluorescence induced by inhomogeneous irradiation was maintained for two months and a suppressed diffusion of the fluorescent dyes in the gel matrix was observed.
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