Radiochromic gels for UV radiation measurements in 3D

In this work, we present for the first time three-dimensional (3D) gel dosimeters for 3D UV dose distribution measurements. These new gel dosimeters are aqueous compositions containing 2,3,5-triphenyltetrazolium chloride or 4,4'-benzylidenebis(N,N-dimethylaniline) (leucomalachite green) and poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F-127), which form a physical gel matrix. The unique feature of these gels is their high transparency and colourlessness, comparable to crystal clear water. This differentiates them from 3D gel dosimeter compositions that are made of gelatine and used for radiotherapy dosimetry purposes only. If UV irradiated, the gels become coloured (red or green); the colour depends on the radiation sensitive compound in the composition. Both gels were examined versus UVA (range: 315-400 nm; a peak at 369 nm), UVB (range: 280-360 nm; a peak at 306 nm) and UVC (253.7 nm) irradiation. The typical parameters of such dosimeters were derived after obtaining their calibrations: linear dose range, dynamic dose range, dose threshold and dose sensitivity, as well as the UV subranges to which the gels were the most sensitive. The 2,3,5-triphenyltetrazolium chloride gels were the most sensitive to UVA radiation, whereas the leucomalachite green gels were sensitive to UVB. The highest dose sensitivity of the gels was obtained for 3 mmol/dm(3) 2,3,5-triphenyltetrazolium chloride and 7 mmol/dm3 leucomalachite green, which amounted to 3.60 +/- 0.12 and 42.85 +/- 1.53 cm(2)/J, respectively (the linear dose range was equal to 0.15-0.9 and 0-0.3 J/cm(2); respectively, and the dynamic dose range was equal to 0-2 and 0-5 J/cm(2), respectively). The 2,3,5-triphenyltetrazolium chloride gels were more sensitive to UVA but less sensitive to UVB and UVC than the leucomalachite green gels. Additionally, the gel dosimeters were examined with respect to their temporal stability, dose response for fractionated and non-fractionated doses as well as the repeatability and spatial stability of the dose distribution. The spatial stability results obtained suggested that 2,3,5-triphenyltetrazolium chloride gels keep the dose distribution integral for over 10 days after irradiation, contrary to the leucomalachite green gels that lose it soon after irradiation. However, this does not disqualify the leucomalachite green gels from use as 3D radiation dosimeters, on the condition that they are measured in 3D soon after irradiation. The proposed gel dosimeters can be used as UV dose sensors, 1D UV dosimeters or 3D high resolution dosimeters. (C) 2017 Elsevier B.V. All rights reserved.