Verification of dose distribution in high-dose-rate brachytherapy using a nanoclay-based radio-fluorogenic gel dosimeter

Abstract

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.

Effects of radical scavengers on nanocomposite Fricke gel for heavy ion beam irradiation

“…For more detailed characterization, it is necessary to improve the sensitivity or change the measurement system. For example, it is useful to investigate the application of a gel dosimeter using the most sensitive fluorescent probe [16][17][18][19][20].…”

Sensitivity enhancement of DHR123 radio-fluorogenic nanoclay gel dosimeter by incorporating surfactants and halogenides

“…For example, we have reported the application to brachytherapy which has a dose distribution having a steep dose gradient by using normal DHR123 uorescent gel dosimeter without sensitizer. 44 Despite the problem of establishing a 2 or 3-dimensional measurement method that maintains the highly sensitive characteristics of this gel dosimeter, it is expected that further applied research on the measuring medical radiation doses and its distribution will proceed.…”

Radio‐fluorogenic nanoclay gel dosimeters with reduced linear energy transfer dependence for carbon‐ion beam radiotherapy

“…A two-dimensional (2D) fluorescence gel scanner (GELSCAN-3; iMeasure Inc., Japan) was used to evaluate the florescence intensity distribution of each DHR123 gel sample after irradiation. 32,46 This device was a commercially available flatbed color scanner incorporating a moving optical array that allowed scanning with a charge coupled device (CCD). Measurements were performed with excitation at 465 nm and a resolution of 0.25 mm/pixel together with a focal length of 6 mm.…”