New radiochromic gel for 3D dosimetry based on Turnbull blue: basic properties

Abstract

The recently developed new radiochromic gel dosimeter based on Turnbull blue dye formed by irradiation (the TBG dosimeter) does not exhibit dose pattern degradation due to diffusion effects as observed in the Fricke-gel dosimeter with xylenol orange incorporated into the gel matrix (the FXG dosimeter). The TBG dosimeter can be easily prepared and its optical properties enable evaluation of the gel's response using the cone-beam optical computed tomography technique. The preparation procedure is described in the paper along with the basic characteristics of the gel, including dose response, dose sensitivity, ageing under different storage conditions, diffusion rates of Turnbull blue and gel density. The measurement of diffusion is described in more detail. The same method was applied to the FXG dosimeter for direct comparison. It was found that the diffusion coefficient of the TBG dosimeter stored at 24 degrees C is less than 4 x 10(-3) mm(2) h(-1) (1sigma confidence level), compared to the value of 7.3 x 10(-1) mm(2) h(-1) (1sigma) of the FXG dosimeter measured at the same temperature. Although the TBG dosimeter is less sensitive than the FXG dosimeter, its diffusion coefficient is practically negligible and, therefore, it offers large potential as a three-dimensional dosimeter for applications encompassing sharp dose gradients such as high-dose-rate brachytherapy.

Comparison of the Convolution algorithm with TMR10 for Leksell Gamma knife and dosimetric verification with radiochromic gel dosimeter

“…A TB gel was prepared, using the procedure suggested by Solc et al It is composed of a gel matrix – 0.25% (w/w) phytagel, 0.5 mM potassium ferricyanide, and 0.5 mM ferric chloride compound dissolved in 1 mM sulphur acid medium. The prepared gel was poured into two glass cylindrical flasks (0.2 l, with a diameter of 6 cm), with one gel sample used for irradiation and one sample for background.…”

“…The optical CT scanner, described in more detail by Solc et al, consisted of a 16‐bit astronomy CCD camera (G2‐0402 type, Moravian Instruments, Czech Republic), stepper motor (65535 micro‐steps per 360 turn), and a light source (a red diode array emitting light at a peek wavelength of 660 nm). Data analysis was performed, using software developed in‐house in the Matlab ® environment (The MathWorks, Inc., Natick, MA, USA), as suggested by Solc et al The reconstructed image had a resolution of 4.2 px/mm.…”

“…A radiochromic gel dosimeter based on Turnbull blue dye formed by irradiation (TB gel) is an integral chemical dosimeter introduced by Solc et al The response can be evaluated, using both cone‐ and laser‐beam optical CT. Basic properties of the TB gel dosimeter are summarized by Solc et al and Vavru et al It offers several advantages such as inhibited diffusion, linear response from 0 Gy up to at least 400 Gy, easy preparation, and nontoxic composition. The main disadvantages of TB gel dosimeters are lower sensitivity that requires a longer irradiation time, and gel aging caused by the spontaneous interactions of ferric ions with organic compounds of the gel.…”

A new spectroscopic method for measuring ferric diffusion coefficient in gelatin-based dosimeter gels

“…Considering the interface as constituted by a homogeneous distribution of ferric ions of concentration c irr that induces a transverse relaxation rate R 2irr in contact with the non-irradiated gel of transverse relaxation rate R , 20 the expression of the transverse relaxation rate is fund by extension of the formule 6:…”

“…Solc et al used the potassium ferricyanide K 3 Fe(CN) 6 and the reduction of the iron(III)citrate by the radiation. This green-yellow fluorescent complex may be combined with iron(II) to obtain the Turnbull blue whose concentration increases as a function of dose [20]. This optical change can be measured with a spectrophotometer for 1D/point dosimetry or an optical CT scanner for 3D dosimetry.…”