The feature of reusability of a gel dosimeter is of particular interest for application to three-dimensional dosimetry in clinical settings. As one of the reusable materials, the radiochromic gel formula composed of polyvinyl alcohol (PVA), glutaraldehyde (GTA), and iodide (I), abbreviated as “PVA-GTA-I gel dosimeter”, is investigated in the present study.
Radiation Measurements 149 (2021) 106674 Contents lists available at ScienceDirect Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas Annealing properties of the PVA-GTA-I gel dosimeter ˜ o a, b, c, Chryzel Angelica B Gonzales a, Akito Saito d, Takuya Wada e, Jolan E Tan Yasushi Nagata f, Hiroshi Yasuda a, * a Department of Radiation Biophysics, Research Institute for Radiation Biology and Medicine (RIRBM), Hiroshima University, Kasumi 1-2-3, Minami-ku, Hiroshima, 734-8553, Japan b Graduate School of Biomedical and Health Sciences, Hiroshima University, Kasumi 1-2-3 Minami-ku, Hiroshima, 734-8553, Japan c Phoenix Leader Education Program (Hiroshima Initiative) for Renaissance from Radiation Disaster, Hiroshima University, Kasumi 1-2-3 Minami-ku, Hiroshima, 7348553, Japan d Department of Radiation Oncology, Hiroshima University Hospital, Kasumi 1-2-3, Minami-ku, Hiroshima, 734-8551, Japan e Section of Radiation Therapy, Department of Clinical Support, Hiroshima University Hospital, Kasumi 1-2-3, Minami-ku, Hiroshima, 734-8551, Japan f Department of Radiation Oncology, Institute of Biomedical and Health Sciences, Hiroshima University Hospital, Kasumi 1-2-3, Minami-ku, Hiroshima, 734-8551, Japan A R T I C L E I N F O A B S T R A C T Keywords: Radiochromic gel dosimeter PVA-GTA-I Annealing LINAC X-rays γ-rays Radiation therapy Reusable The feature of reusability of a gel dosimeter is of particular interest for application to three-dimensional dosimetry in clinical settings As one of the reusable materials, the radiochromic gel formula composed of polyvinyl alcohol (PVA), glutaraldehyde (GTA), and iodide (I), abbreviated as “PVA-GTA-I gel dosimeter”, is investigated in the present study The annealing properties of the PVA-GTA-I gel were examined for energetic Xrays from a medical linear accelerator, while its reusability was confirmed for 137Cs-source γ-rays The radiationinduced colorings of the PVA-GTA-I gel irradiated with few Gy were erased within several hours, while the reactions induced by higher dose (~20 Gy) were more persistent and required longer time up to 24 h to be completely reversed The linear dose response of the PVA-GTA-I dosimeter was well reproduced after repetition of annealing Introduction Gel dosimeters are chemically-based materials that allow 3D dose distribution analysis due to their unique characteristic of recording spatial dose information within its medium (Baldock et al., 2010; Romanyukha et al., 2011; Schreiner, 2015) This attribute is of great importance in the dosimetry and quality assurance of modern radiation therapy plans, where current and emerging techniques require more accurate methods to quantify ionizing radiation fields in three di mensions (3D) In recent studies, there have been considerable interests in the development and improvement of radiochromic gel dosimeters that rely on the radiation-induced color transformation which is pro portional to the absorbed dose (Solc and Spvek, 2009; Vandecasteele et al., 2011; Nasr et al., 2015; Oldham, 2015; Colnot et al., 2018; Kouvati et al., 2019) Using these materials couple with optical techniques such as spectrophotometry or optical computed tomography (optical CT), the 3D radiation dose distribution in a human tissue or organ could be approximately measured ˜ o et al., 2019, 2020), we investigated the In our earlier studies (Tan rudimentary dose-response characteristics of an experimental radio chromic gel formula for 137Cs-source γ-rays The formula is composed of mostly water, polyvinyl alcohol (PVA) crosslinked with glutaraldehyde (GTA), potassium iodide (KI), fructose, and glucono-δ-lactone (GDL), which was abbreviated as the ‘PVA-GTA-I gel dosimeter’ The PVA-GTA-I gel dosimeter was developed through modification of the polyvinyl alcohol-iodide (PVA-I) based gel (Miyoshi et al., 2016; Suna gawa et al., 2017; Hayashi et al., 2019, 2020) in conjunction with glutaraldehyde (GTA) as a cross-linking agent which was applied to Fricke-gels (d’Errico et al., 2017; Marini et al., 2017) This PVA-GTA-I gel dosimeter converts from transparent to color red after irradiation It is relatively easy to fabricate and has high transparency and sensi tivity Moreover, this gel formula could be reinitialized through ˜ o et al., 2019) annealing, as qualitatively confirmed by the authors (Tan This feature is comparable to the PRESAGE-RU radiochromic plastic formulation which was also reported to have potential reusability through the rapid decay of its coloration in dark storage and room temperature conditions (Juang et al., 2015) In the PVA-GTA-I gel, the main cause of color loss is through heating which results in the * Corresponding author E-mail address: hyasuda@hiroshima-u.ac.jp (H Yasuda) https://doi.org/10.1016/j.radmeas.2021.106674 Received 24 June 2021; Received in revised form September 2021; Accepted 20 October 2021 Available online 25 October 2021 1350-4487/© 2021 The Authors Published by Elsevier Ltd This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) J.E Ta˜ no et al Radiation Measurements 149 (2021) 106674 Fig Irradiation (a) set-up and (b) geometric dimensions of the PVA-GTA-I gel samples using X-rays from the 6-MV medical linear accelerator (LINAC) separation or dissociation of the triiodide ions (I3− ) and the PVA-GTA complex Additionally, the presence of the sugar (i.e., fructose) further reduces the I3− to mono iodide ions (3I− ) which finally leads to the reinitialized or colorless state of the gel Since it is only in more recent years that the PVA-GTA-I gel is found to have such advantageous characteristics, further research is needed in terms of the quantitative analyses of the annealing properties Thus, in the present study, the authors focus on further investigating the annealing properties of the PVA-GTA-I gel dosimeter, expecting that a practical method to reinitialize the dosimeter between the fractions of dose delivery to radiotherapy patients will be established More concretely, we analyze the absorbance changes with the investigation of the effect of natural oxidation on the annealed gel samples, trying to provide possible implications towards its application for radiation therapy irradiation set-up and the measurement duration, three separate solu tions of the same PVA-GTA-I gel formula were fabricated The annealing schedule was divided into three batches: the first batch for 0.25, 0.5, 0.75 and 1.0 h annealing; the second batch for 4, 8, and 10 h annealing; and the third batch for 12, 16, 20, and 24 h annealing Each annealing time has a corresponding set of samples which comprises 27 cuvette samples (i.e., three cuvette samples for each dose level) A total of 297 cuvette samples of the PVA-GTA-I gel dosimeter were prepared for these experiments The dose-responses of the three sample batches were also analyzed to check the fabrication reproducibility 2.2 Medical linear accelerator irradiation The irradiations of the PVA-GTA-I gel dosimeters were conducted using a 6-MV high-energy photon beam produced by TrueBeam™ medical linear accelerator (LINAC) (Varian Medical Systems, CA, USA) located at Hiroshima University Hospital (Hiroshima, Japan) As illus trated in Fig 1, the gel dosimeters were positioned perpendicular to the beam axis and in between solid water-equivalent phantoms (PH-40 Tough Water Phantom®, Kyoto Kagaku Co., Ltd., Kyoto, Japan) The source-to-skin distance (SSD) and source-to-axis distance (SAD) were 98.4 cm and 100 cm, respectively The irradiation field size was 15 × 15 cm2, and a fixed dose rate at 600 MU⋅min− was employed The gel dosimeters were irradiated with photon beams at dose levels of 1, 2, 3, 4, 7, 10, 15, and 20 Gy with one set of samples left unirradiated (con trol) Shortly after irradiation, all the samples were stored inside the refrigerator at 15 ◦ C for about 24 h Following this, the samples were then stabilized at room temperature for h before performing the initial measurements Materials and methods The methods used in this study comprised of preparation of the PVAGTA-I gel dosimeter samples, irradiation of the samples using high en ergy X-rays and annealing the irradiated samples at a selected temper ature wherein the absorbance decays were then quantitatively measured While, the same-composition material was irradiated with 137 Cs-source γ-rays for confirmation of its reusability 2.1 Gel sample preparation The synthesis of the gel samples was performed by first dissolving 10 wt % of partially saponified polyvinyl alcohol (PVA) (86–90 mol% saponification, polymerization degree = 1000) in Milli-Q™ ultrapure water (resistivity = 18.2 M Ω cm) The potassium iodide (KI), fructose, glucono-δ-lactone (GDL), and 25% aq glutaraldehyde (GTA) with con centrations of 1.42, 1.54, 1.53, and 0.36 wt %, respectively, were then added into the PVA solution at room temperature (20 ◦ C) until a ho mogeneous mixture was achieved All the reagents used were of analytical grade from FUJIFILM Wako Pure Chemical Corporation (Osaka, Japan) The resulting liquid solution was transferred into the uncovered PMMA cuvettes (10 × 10 × 45 mm3) and placed inside a vacuum chamber (− 0.08 MPa) for h to inhibit the formation of air pockets within the gel samples After removing from the vacuum, the cuvette samples were covered with lids and parafilm to minimize water loss during the subsequent heating process (i.e., for gel solidification) The samples were heated at 50 ◦ C for 12 h in a sterilizing oven (Sanyo MOV-112S, Sanyo Electric Biomedical Co., Ltd., Osaka, Japan) and then stabilized at room temperature for h before irradiation For preparation of a large number of samples and limitations in the 2.3 Absorbance measurement and annealing process The measurements of the optical absorbances were conducted using a NanoDrop OneC™ UV–Vis spectrophotometer (Thermo Fisher Scien tific Inc., MA, USA) The absorbance value at the 486 nm peak was used as the reference point for all the results in the present study Following initial measurements, the PVA-GTA-I gel dosimeter samples were immediately annealed in a pre-heated oven at 50 ◦ C with time intervals of 0.25, 0.5, 0.75, 1, 4, 8, 10, 12, 16, 20, and 24 h The gel dosimeters were always stabilized at room temperature for h before the UV–Vis measurements The change of absorbance (ΔAbs) was obtained from the difference between the measured absorbance of the irradiated sample (Absi ) and unirradiated (control) sample (Absc ), as defined in Eq (1): ΔAbs = Absi –Absc (1) J.E Ta˜ no et al Radiation Measurements 149 (2021) 106674 Fig Irradiation set-up of the PVA-GTA-I gel samples using the source γ-rays 137 Fig Dose vs ΔAbs plots of the three batches of gel samples fabricated with the same PVA-GTA-I gel formula Linear fitting was applied to each batch; the error bar represents s.d Cs- Canada) The experimental set-up is shown in Fig The gel dosimeters were positioned at the center of the sample container (φ 260 × 100 mm) perpendicular to the sources Three sets of irradiations were performed to the PVA-GTA-I gel dosimeters for six dose levels: 1, 2, 3, 5, 7, and 10 Gy with the dose rate of 0.806 Gy min− Soon after each succeeding irradiations and measurements, the samples were annealed repeatedly for 12 h at 50 ◦ C for the reinitialization process All samples were stored inside the refrigerator at ◦ C in between multiple irradiations and measurements It should be noted that high-energy X-rays were not used for the reusability test due to the limited access in the facility caused by the COVID-19 pandemic, hence the 137Cs γ-ray source were used as an alternative radiation source which was more accessible Results and discussion 3.1 Fabrication reproducibility The photographic images of the PVA-GTA-I gels irradiated with (control), 1, 2, 3, 4, 7, 10, 15 and 20 Gy of LINAC X-rays and annealed for (before starting), 1, 12 and 24 h are shown in Fig It was visually confirmed that the radiation-induced colorings of the PVA-GTA-I do simeters were reversed to the initial state after 24 h at longest Fig shows the dose- ΔAbs plots of the three batches of the PVAGTA-I gel dosimeter The dose-response was linear for all batches with average Re = 0.99 and the average sensitivity defined by the slope (the m value indicated in the figure) was around 0.035 Gy-1 The small varia tions in sensitivity could be attributable to several factors such as at mospheric temperature and humidity during the storage and stabilization stages Table shows the summary of the one-way ANOVA test which was conducted to examine difference between the ΔAbs values among the different PVA-GTA-I gel batches A p-value of less than 0.05 was required to reject the null hypothesis H0 The result of the ANOVA (F(2,24) = 0.0085, P = 0.99), which did not reject the H0, confirmed the good reproducibility in fabrication of the different batches of PVA-GTA-I gels Fig Images of the PVA-GTA-I gels irradiated with (control), 1, 2, 3, 4, 7, 10, 15 and 20 Gy of 6-MV LINAC X-rays at 0h, 1h, 12h and 24 h of annealing duration All the samples were stored in a refrigerator after irradiation until the annealing was started 2.4 Reusability test with 137 Cs-source γ-rays 3.2 Behavior of the annealing decay curve Reusability of the PVA-GTA-I gels having the same composition was examined using 137Cs source γ-rays from the Gammacell®40 Exactor Low Dose Rate Research Irradiator (Best Theratronics Ltd., Ottawa, Fig presents the ΔAbs with respect to annealing time of the PVAGTA-I gel dosimeters irradiated with different doses Each data point J.E Ta˜ no et al Radiation Measurements 149 (2021) 106674 Table Summary of one-way ANOVA test for the fabrication reproducibility SUMMARY Groups Count Sum Average Variance Batch Batch Batch 9 2.051889 2.182519 2.146694 0.227988 0.242502 0.238522 0.056427 0.062168 0.059264 Source of Variation SS df MS F P-value F crit Between Groups Within Groups Total 0.001012 1.422867 1.42388 24 26 0.000506 0.059286 0.008538 0.991501 3.402826 ANOVA Table Fitting parameters (see equation (2)) and goodness-of-fit values for each dose level of the PVA-GTA-I gel dosimeters annealed at 50 ◦ C for up to 24 h Fitting parameters + A2 e(− λ2 *t) λ1 (h− 1) A2 (arb unit) λ2 (h− 1) A1/ A2 ratio R2 χ2 0.0442 3.33 – – 0.946 0.0846 3.33 0.0057 0.006 14.8 0.997 0.1112 3.33 0.0259 0.468 4.30 0.993 0.1225 3.33 0.0648 0.478 1.89 0.997 0.1927 3.33 0.1508 0.335 1.28 0.997 10 0.2035 3.33 0.2924 0.245 0.70 0.998 15 0.2815 3.33 0.4718 0.156 0.60 0.996 20 0.2146 3.33 0.7749 0.118 0.28 0.996 1.65 × 10− 4.04 × 10− 2.70 × 10− 2.40 × 10− 8.89 × 10− 1.35 × 10− 5.26 × 10− 1.05 × 10− (χ2) values were also calculated The values of those parameters are summarized in Table Additionally, the absorbance half-life was determined from the decay coefficient by Eq (3): is an average of three samples with three measurement series obtained at the 486 nm peak The error bars shown in the plot represent one stan dard deviation (1 s.d.) that were mostly located within the data markers It was found that the time changes of ΔAbs values be fitted well with a two-phase exponential decay function, as described by Eq (2): λ1 *t) A1 (arb unit) Note: The parameter values in this table correspond to Eq (2) in the text and the fitting curves in Fig 5; A1 & λ1 correspond to the fast component and A2 & λ2 the slow component; R2 and χ2 are the coefficient of determination and chi-square value, respectively Fig Annealing time vs ΔAbs plots of the PVA-GTA-I gel dosimeters irradi ated with doses from to 20 Gy The inset graph shows the magnified view of the lower dose region (1–4 Gy) Each dose level is fitted with the two-phase decay function and is represented by the line Note that the ΔAbs values were normalized from to for illustration purposes A(t) = A1 e(− Goodness-of-fit Dose (Gy) Tn = ln λn (3) where Tn and λn are the half-life and decay coefficient at a given phase order n (n = or 2), respectively From the results shown in Fig and Table 2, it was found that the annealing decay curves of the ΔAbs of the PVA-GTA-I gel dosimeters can be approximated well with the two-phase decay model It was seen that the contribution ratio of the fast decay component to slow decay component (i.e, A1/A2) became smaller with increasing dose level; it was considered that the contribution of the slow decay component was negligible for Gy or less The average half-life (T2 ) of the slow decay component calculated by Eq (3) for Gy or higher dose ranged from 1.5 h for Gy to 5.9 h for 20 Gy, while T1 was constant as 12 Further (2) where A(t) is the absorbance at a given time t; A1 and A2 are the am plitudes of each decay phase; and λ1 and λ2 are the fast and slow decay constants, respectively Through the careful regression analyses, it was found that the value of λ1 could be given as a constant (= 3.33); the other three parameters (A1 , A2 and λ2 ) were judged to be variable quantities and then determined by the least-squares method Additionally, to verify the goodness-of-fit, the coefficient of determination (R2) and chi-square J.E Ta˜ no et al Radiation Measurements 149 (2021) 106674 Fig Annealing time vs ΔAbs subplots of the PVA-GTA-I gel samples measured soon after annealing (black marker) and 7d after annealing (red marker) for different dose levels Each point is the average ΔAbs from three samples and the error bar represents s.d (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) analysis of the two-phase decay model reveals the estimated annealing time for the effective reinitialization (i.e., normalized ΔAbs ≤ 0.003) of the irradiated gel samples: Gy ≈ 1h, Gy ≈ 1.25h, Gy ≈ 4.75h, Gy ≈ 6.5h, Gy ≈ 11.75h, 10 Gy ≈ 18.75h, 15 Gy ≈ 32.5h, 20 Gy ≈ 47.25h These results suggest that the radiation-induced coloring in the PVAGTA-I gel dosimeter is erased quickly at the lower dose range (~few Gy) by annealing, whereas the reactions induced by highly dense ioni zation (~20 Gy) are more persistent and require a longer time to be completely reversed 3.3 Auto-oxidation days post-annealing The natural oxidation in the PVA-GTA-I gel dosimeter was measured after days had elapsed post-annealing The results are shown in Fig in which subplots of the ΔAbs values from the gel dosimeter samples measured soon (~2h) after annealing (black marker) and 7d after annealing (red marker) for different dose levels The error bars represent s.d The purpose of this subplots was to confirm if the gel dosimeter is effectively reinitialized since previous observations from unpublished experiments showed that the PVA-GTA-I gel dosimeter (especially those irradiated >10Gy) tend to have residual absorbance after annealing To further elaborate, a freshly annealed PVA-GTA-I gel dosimeter is color less in visual inspection and displayed an absorbance value comparable to an unirradiated dosimeter after the spectrophotometry measurement However, the gel coloration “relapsed” within several hours or days, which indicated that the gel is not sufficiently annealed and that some slow decay components are still present In the context of the data presented in the study, the contrast of the ΔAbs values between the 2h and 7d post-annealing measurements provides further evidence in the effective reinitialization time of the PVA-GTA-I gel dosimeter for each dose level For instance, in the 10 Gy sample measured soon after annealing, the ΔAbs values from 12 to 24h of annealing are all ≤0.003 However, measuring the sample again 7d after annealing reveals that the ΔAbs at the 12h annealing point significantly increased to 0.024, while those annealed from 16h to 24h maintained their values within ≤0.003 This observation implies that 12h of annealing at 50 ◦ C is not enough to effectively reinitialize the PVA-GTA-I gel In general, the PVA- Fig Results of the reusability test of the PVA-GTA-I gel dosimeter The same samples were irradiated repeatedly with 137Cs-source γ-rays (1, 2, 3, 5, 7, 10 Gy) after annealing All the samples were stored in the refrigerator for ◦ C between irradiations and measurements GTA-I gel dosimeters irradiated with few Gy were reinitialized in several hours, while those with higher doses (~20 Gy) needed a longer time up to 24 h Thus, it is commonly recommended to apply the annealing condition of 24 h at 50 ◦ C to erase the colorings of the PVA-GTA-I gel dosimeters irradiated with a fractionated delivering dose in radiation therapy J.E Ta˜ no et al Radiation Measurements 149 (2021) 106674 3.4 Confirmation of reusability 17K09072 and 18KK0417) Fig shows the dose responses of the PVA-GTA-I gels that were irradiated with 137Cs source γ-rays repeatedly after annealing Each data point is an average and the error bar is one standard deviation of the data obtained from three samples; most of the error bars were located within the data markers As expected from the preceding study using a ˜ o et al., 2019), the linear dose similar-composition PVA-GTA-I gel (Tan response up to 10 Gy was reproduced well after repetition of annealing; the sensitivities were 3.9 × 10− 2, 3.9 × 10− 2, and 4.0 × 10− for the first, second, and third irradiation, respectively Accordingly, it is considered that the PVA-GTA-I gels developed in the present study could be used repeatedly at least three times by application of an appropriate annealing process References Baldock, C., De Deene, Y., Doran, S., Ibbott, G., Jirasek, A., Lepage, M., McAuley, K.B., Oldham, M., Schreiner, L.J., 2010 Polymer gel dosimetry Phys Med Biol 55 https://doi.org/10.1088/0031-9155/55/5/R01 Colnot, J., Huet, C., Gschwind, R., Clairand, I., 2018 Characterisation of two new radiochromic gel dosimeters TruViewTM and ClearViewTM in combination with the vistaTM optical CT scanner: a feasibility study Phys Med 52, 154–164 https://doi org/10.1016/j.ejmp.2018.07.002 d’Errico, F., Lazzeri, L., Dondi, D., Mariani, M., Marrale, M., Souza, S.O., Gambarini, G., 2017 Novel GTA-PVA Fricke gels for three-dimensional dose mapping in radiotherapy Radiat Meas 106, 612–617 https://doi.org/10.1016/j radmeas.2017.07.003 Hayashi, S., Ono, K., Fujino, K., Fujimoto, S., 2019 Influence of the components of a radiochromic PVA – iodide gel dosimeter on the optical dose response J Phys Conf Ser 1305, 012031 https://doi.org/10.1088/1742-6596/1305/1/012031 Hayashi, S., Ono, K., Fujino, K., Ikeda, S., Tanaka, K., 2020 Novel radiochromic gel dosimeter based on a polyvinyl alcohol – iodide complex Radiat Meas 131, 106226 https://doi.org/10.1016/j.radmeas.2019.106226 Juang, T., Adamovics, J., Oldham, M., 2015 Characterization of a reusable PRESAGE® 3D dosimeter J Phys Conf Ser 573, 6–11 https://doi.org/10.1088/1742-6596/ 573/1/012039 Kouvati, K., Jaszczak, M., Papagiannis, P., Kadlubowski, S., Wach, R., Maras, P., Dudek, M., Kozicki, M., 2019 Leuco crystal violet-Pluronic F-127 3D radiochromic gel dosimeter Phys Med Biol 64, 175017 https://doi.org/10.1088/1361-6560/ ab2f5d Marini, A., Lazzeri, L., Cascone, M.G., Ciolini, R., Tana, L., D’Errico, F., 2017 Fricke gel dosimeters with low-diffusion and high-sensitivity based on a chemically crosslinked PVA matrix Radiat Meas 106, 618–621 https://doi.org/10.1016/j radmeas.2017.02.012 Miyoshi, H., Masahiko, Y., Maeda, S., Yamada, K., Matsumura, J., 2016 Reversible radiochromic plate based on polyvinyl alcohol-iodide complex containing silica nanoparticles J Radioanal Nucl Chem 308, 469–475 https://doi.org/10.1007/ s10967-015-4465-y Nasr, A.T., Alexander, K.M., Olding, T., Schreiner, L.J., McAuley, K.B., 2015 Leucocrystal-violet micelle gel dosimeters: II Recipe optimization and testing Phys Med Biol 60, 4685–4704 https://doi.org/10.1088/0031-9155/60/12/4685 Oldham, M., 2015 Radiochromic 3D detectors J Phys Conf Ser 573 https://doi.org/ 10.1088/1742-6596/573/1/012006 Romanyukha, A., Trompier, F., Reyes, R.A., Melanson, M.A., 2011 EPR measurements of fi ngernails in Q-band Radiat Meas 46, 888–892 https://doi.org/10.1016/j radmeas.2011.04.004 Schreiner, L.J., 2015 True 3D chemical dosimetry (gels, plastics): development and clinical role J Phys Conf Ser 573 https://doi.org/10.1088/1742-6596/573/1/ 012003 Solc, J., Spvek, V., 2009 New 3D radiochromic gel dosimeters with inhibited diffusion J Phys Conf Ser 164, 1–7 https://doi.org/10.1088/1742-6596/164/1/012047 Sunagawa, T., Harvel, G., Aoki, Y., Umeda, M., Hayami, J., Sakakibara, K., Goto, H., Ebina, T., Taguchi, M., Nagasawa, N., Yoshihashi, S., Hatashita, M., Kume, K., Sakura, T., 2017 Development of the gel indicator using PVA and KI Mem Fukui Univ Technol 47, 105–110 (in Japanese) Ta˜ no, J., Hayashi, S., Hirota, S., Gonzales, C.A., Yasuda, H., 2019 Development of a reusable PVA-GTA-I gel dosimeter for 3D radiation dose assessments J Phys Conf Ser 1305 https://doi.org/10.1088/1742-6596/1305/1/012034 Ta˜ no, J.E., Hayashi, S i, Hirota, S., Gonzales, C.A.B., Yasuda, H., 2020 Effect of the glucono-δ-lactone concentration on the sensitivity and stability of PVA-GTA-I radiochromic gel dosimeter Radiat Meas 134 https://doi.org/10.1016/j radmeas.2020.106311 Vandecasteele, J., Ghysel, S., Baete, S.H., Deene, Y De, 2011 Radio-physical properties of micelle leucodye 3D integrating gel dosimeters Phys Med Biol 56, 627–651 https://doi.org/10.1088/0031-9155/56/3/007 Conclusions In the present study, the annealing properties of the PVA-GTA-I gel dosimeter were quantitatively examined for the first time As a result, it was found that the annealing responses of PVA-GTA-I gel dosimeters irradiated with X-rays of up to 20 Gy from a medical linear accelerator could be well approximated with two-phase exponential decay func tions The radiation-induced colorings at few Gy were easily erased in several hours, whereas a longer annealing time of up to 24 h was required for reinitializing the samples irradiated with a higher dose The identical, linear dose response was well maintained after repeated annealing processes for γ-ray irradiation These findings will be an important basis for using the PVA-GTA-I gel dosimeter as a tool for dosimetry in radiation therapy The feature of reusability of this novel dosimeter is favorable as it opens the prospect of routine use in clinical settings where multiple, detailed dose verifications need to be per formed For establishing a practical use of the PVA-GTA-I gel dosimeter as part of the general protocol of radiation therapy, it is highly recom mended to conduct further studies to clarify the possible extent of its repeated use and the best storage conditions that can minimize the natural oxidation as well as the fundamental physico-chemical mecha nisms behind the annealing effects observed Research in the quest for resolutions on these subjects is currently underway Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper Acknowledgments The authors would like to thank the staff of the Department of Ra diation Oncology of Hiroshima University Hospital for their technical support This work was supported by the JSPS KAKENHI (Grant Number ... study, the authors focus on further investigating the annealing properties of the PVA-GTA-I gel dosimeter, expecting that a practical method to reinitialize the dosimeter between the fractions of. .. implies that 12h of annealing at 50 ◦ C is not enough to effectively reinitialize the PVA-GTA-I gel In general, the PVA- Fig Results of the reusability test of the PVA-GTA-I gel dosimeter The same samples... found that the annealing decay curves of the ΔAbs of the PVA-GTA-I gel dosimeters can be approximated well with the two-phase decay model It was seen that the contribution ratio of the fast decay