This work presents an improvement of the VIPAR ^nd (‘nd’ stands for ‘normoxic, double’, or VIP) polymer gel dosimeter. The gel composition was altered by increasing the concentration of the monomeric components, N -vinylpyrrolidone (NVP) and N , N ′-methylenebisacrylamide (MBA), in co-solvent solutions. The optimal composition (VIPAR ^CT , where ‘CT’ stands for computed tomography, or VIC) comprised: 17% NVP, 8% MBA, 12% t-BuOH, 7.5% gelatine, 0.007% ascorbic acid, 0.0008% CuSO ₄ × 5H ₂ O and 0.02% hydroquinone. The following characteristics of VIC were achieved: (i) linear dose range of 0.9 ^_ 30 Gy, (ii) saturation for radiation doses of over 50 Gy, (iii) threshold dose of about 0.5 Gy, (iv) dose sensitivity of 0.171 Gy ⁻¹ s ⁻¹ , which is roughly 2.2 times higher than that of VIP (for nuclear magnetic resonance measurements). It was also found that VIC is dose- rate-independent, and its dose response does not alter if the radiation source is changed from electrons to photons for external beam radiotherapy. The gel responded similarly to irradiation with small changes in radiation energy but was sensitive to larger energy changes. The VIC gel retained temporal stability from 20 h until at least 10 d after irradiation, whereas spatial stability was retained from 20 h until at least 6 d after irradiation. The scheme adopted for VIC manufacturing yields repeatable gels in terms of radiation dose response. The VIC was also shown to perform better than VIP using x-ray computed tomography as a readout method; the dose sensitivity of VIC (0.397 HU Gy ⁻¹ ) was 1.5 times higher than that of VIP. Also, the dose resolution of VIC was better than that of VIP in the whole dose range examined.

This work discusses the substitution of a gelatine physical gel matrix with a matrix made of poly(ethylene oxide)- block -poly(propylene oxide)- block -poly(ethylene oxide) (Pluronic F-127) in five 3D radiotherapy polymer gel dosimeters: MAGAT, PAGAT, NIPAM, VIPAR ^nd (VIP) and VIPAR ^CT (VIC). The current research outcomes showed that not each polymer gel dosimeter could be manufactured with Pluronic F-127. Two of the polymer gel dosimeters (PAGAT and VIP) containing the Pluronic F-127 matrix allowed for some proper dose response for radiotherapy dosimetry (a response to a dose range of e.g. 0‒50 Gy). The new best performing Pluronic-based polymer gel dosimeters were characterised by improved nuclear magnetic resonance properties, when being compared to gels with gelatine matrix at the same monomer content. These are: (i) a ~33% higher dose sensitivity; (ii) a comparable or slightly higher linear and dynamic dose range and (iii) a lower (new VIP composition, VIP3) or equivocal (new PAGAT composition, PAGAT2-Pluronic) dose threshold. However, there might be optimised gelatine based polymer dosimeters demonstrating even better sensitivity. UV–vis spectrophotometry measurements revealed that Pluronic matrices ensure six-times lower (VIP3–Pluronic) and eight-times lower (PAGAT2-Pluronic) absorbance (at 400 nm) of non-irradiated gels compared to gelatine matrices, which makes the new polymer gel dosimeters optically improved in comparison to their corresponding gelatine-based compositions. The differences in absorption reduce for higher wavelengths. Differential scanning calorimetry measurements revealed the following temperature stability ranges for the gels: (i) VIP with gelatine matrix: 0 °C‒26 °C, (ii) VIP3 with Pluronic matrix: 13.8 °C–55.2 °C, (iii) PAGAT2 with gelatine matrix: 0 °C–80 °C and (iv) PAGAT2 with Pluronic matrix: 21.4 °C–55.2 °C. In conclusion, Pluronic F-127 is an attractive co-polymer to serve as a substitute for the gelatine matrix in some 3D polymer gel dosimeters.

This work reports results related to the manufacturing and optimisation of a leuco crystal violet (LCV)-Pluronic F-127 radiochromic gel dosimeter suitable for 3D radiotherapy dosimetry. A feature of this gel is that the natural gelatine polymer, which is most often used as a matrix in 3D dosimeters, is substituted with Pluronic F-127 synthetic copolymer (poly(ethylene oxide)- block -poly(propylene oxide)- block -poly(ethylene oxide). Pluronic F-127 ensures a higher transparency than gelatine, which may be beneficial for optical computed tomography readout, and improves the thermal properties in the temperature range above ~30 °C at which the gelatine physical gel converts to a solution. The optimal composition obtained comprises 2 mM LCV, 4 mM 4-(1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol (Triton X-100), 17 mM trichloroacetic acid (TCAA) and 25% Pluronic F-127. Its main dose-response features are 4‒150 Gy linear dose range (150 Gy was the maximal dose applied to gels in this work), 0.0070 Gy ⁻¹ cm ⁻¹ dose sensitivity (derived from absorbance (600 nm) = f (dose) for 6 MeV electrons, 0.88(3) Gy s ⁻¹ and 0.0156 Gy ⁻¹ cm ⁻¹ derived from optical density (Δ µ ) = f (dose) for 6 MV x-rays, 0.1010 Gy s ⁻¹ ), low initial colour (initial absorbance = 0.0429) and a diffusion coefficient of crystal violet (CV) in LCV-Pluronic of 0.054 ± 0.023 mm ² h ⁻¹ . Raman spectroscopy was used to characterize LCV-Pluronic chemical changes after irradiation. Differential scanning calorimetry (DSC) revealed that LCV-Pluronic is stable in temperatures between approximately 11 °C and 56 °C. Irradiation of LCV-Pluronic gel impacts on its first sol-gel transition temperature and the thermal effect of this process—both increased with absorbed dose, which might be related to the degradation of Pluronic. LCV-Pluronic is a promising 3D dosimeter for ionising radiation applications. Further work is needed to improve LCV-Pluronic response in the low dose region, and characterize potential effects of pH, temperature during irradiation, and radiation quality/dose rate on dose response characteristics.

This work reports on the impact of tetrakis(hydroxymethyl)phosphonium chloride (THPC) on the properties of a VIC gel dosimeter (VIC is an abbreviated acronym of VIPAR ^CT ). THPC was used as a substitute oxygen scavenger in VIC (17% N -vinylpyrrolidone, 8% N , N ′-methylenebisacrylamide, 12% tert-butyl alcohol, 7.5% gelatine, 0.02% hydroquinone and an oxygen scavenger of 0.007% ascorbic acid and 0.0008% CuSO ₄ × 5H ₂ O). THPC reduced the gelation time of VIC from hours to minutes. The best composition (VIC-T) contained 14 mM THPC and a reduced gelatine concentration (5%) with respect to VIC, which allowed for gelation in about 3 min. VIC-T was characterised by the same dose sensitivity (0.176 ± 0.003 Gy ⁻¹ s ⁻¹ for VIC-T and 0.171 ± 0.002 Gy ⁻¹ s ⁻¹ for VIC), dose threshold (0.5 Gy) and dynamic dose range (0.5‒50 Gy) as VIC, and a lower linear dose range (20 Gy for VIC-T, 30 Gy for VIC) (0.47 T NMR measurements). VIC-T was stable for at least 10 days after irradiation, and 3D dose distribution was stable for over 4 months after irradiation. The dose response of VIC-T was independent of the radiation dose rate, type and energy of radiation for 6 and 15 MV photons and 12 MeV electrons. This is an improvement with respect to VIC which showed a different dose response for 6 MV photons than for 12 MeV electrons and 15 MV photons. Raman spectroscopy showed similarity in the rate of radiation-induced conversion of monomers in VIC and VIC-T, indicating interaction of THPC with gelatine in VIC-T, and showed ageing of gelatine in both dosimeters. Differential scanning calorimetry showed VIC-T stability at 0 °C–80 °C (VIC: 0 °C‒29.5 °C). The chemical polymerisation and crosslinking of gelatine with THPC is reported, the mechanism of which was analysed in detail. A comparison of N -vinylpyrrolidone-containing dosimeters is presented in this work.

This work reports on the surface-modified woven fabrics for use as UV radiation sensors. The cotton and polyamide fabrics were printed with radiochromic hydrogels using a screen-printing method. The hydrogels used as a printing paste were composed of water, poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F-127) as a gel matrix and nitro blue tetrazolium chloride as a radiation-sensitive compound. The development of the hydrogels’ colour occurs after exposure to UV radiation and its intensity increases with increasing absorbed dose. The features of the NBT-Pluronic F-127 radiochromic hydrogels and the fabrics printed with the hydrogels were examined using UV-Vis and reflectance spectrophotometry as well as scanning electron microscopy (SEM). The effects of NBT concentration and UV radiation type (UVA, UVB, UVC) on dose responses of the hydrogels and printed fabrics were also examined. The results obtained reveal that the fabrics printed with NBT-Pluronic F-127 hydrogels can be potentially useful as UV radiation sensors.

NVP-containing three-dimensional polymer gel dosimeters for radiotherapy dosimetry have been developed for more than 20 years. There have been 11 main modifications of the originally proposed VIPAR polymer gel dosimeter that altogether have amounted to 12 gel dosimeter formulae. This communication is to summarise the main chemical changes made to the VIPAR dosimeter over these years of research. The newest NVP-polymer gel dosimeters are also introduced.