A Report on “Radiation Disaster Recovery Studies”
Course: Radiation Disaster Medicine
Name: Jolan Evangelista TañooRegarding “Radiation Disaster Recovery Studies”

It has been a decade since the catastrophic earthquake and tsunami off the Pacificcoast of Japan, which consequently damaged the Fukushima Daiichi Nuclear Power Plant(FDNPP), releasing the most significant quantity of radioactive nuclides in the environment
since the 1986 Chernobyl nuclear disaster[1]. Numerous people were displaced from theirhomes, and significant concerns on the safety and well-being of Japanese society were raised.
These concerns revolved around the health-related effects of radiation, food safety,
psychological impact, and environmental contamination[2]. Considering the global influence
and wide range of issues that have emanated from this radiation disaster, it is essential tohave experts in various fields of study capable of leading the recovery efforts with soundjudgment and strong mental fortitude.
Developing such global leaders in response to radiation disasters is the aim of the
Phoenix Leader Education Program (PLEP). I am grateful and privileged to be part of sucha unique program that promotes the basic philosophies of radiation disaster response andinterdisciplinary collaboration among professionals of different disciplines. The PLEP
ensures these goals are achieved through comprehensive foundation subjects, crossdisciplinary coursework, internships, fieldwork, and technical training courses by experts inJapan and abroad. Through research symposiums, seminars, and dialogues, the leadershipand teamwork among the Japanese and international students with different educational
backgrounds are also fostered by PLEP. As a PLEP student for four years, I gained
considerable insights into the importance and application of my academic background (i.e.,
medical physics) in the field of radiation disaster response and recovery. My previous medical
physics coursework comprised topics in radiation dosimetry, radiation biology,
instrumentation, and health physics, all of which are pertinent subjects in radiological or
nuclear disasters. However, my knowledge of the appropriate preparation, handling, andrecovery measures in large-scale radiological emergencies was still limited. Being part of the
PLEP provided the necessary education and training to apply my radiation disaster response
and recovery expertise. For instance, our training courses covered the theoretical backgroundof radiation disaster response and its application by performing fully-equipped practicalsessions that involve medical management, radiological surveys, and decontamination
methods in radiological or nuclear emergency scenarios. These exercises were engaging andtested our technical knowledge in radiation protection and disaster response and our effective
communication, decision-making, and teamwork abilities. I also had the opportunity toparticipate in numerous international symposiums and conferences. In these events, I
learned about the diverse topics and issues involving radiation disaster recovery, met worldrenowned experts, and established connections among colleagues in various scientific fields.
Building excellent rapport with other experts and colleagues and expanding one’s network isa critical aspect of being a global leader in radiation disaster preparedness and recovery.
1Additionally, our practical skills were strengthened through fieldwork and internshipactivities with local and international organizations, research institutes, universities, andprivate companies, which are part of the collaborating system of the PLEP. The fieldwork
activities include community immersions, facility visits, lectures, and interviews. These
hands-on experiences gave me a more robust understanding of the actual status of recovery,
persisting issues, and the resilience of the affected communities in the aftermath of thenuclear accident. In my long-term internship, the partner organization was the National
Institutes for Quantum and Radiological Science and Technology (QST·NIRS). I acquired
relevant information on radiation dosimetry audits using glass dosimeters and heavy-ion
beam irradiation systems, and performed research collaboration experiments using my gel
dosimeter formula.
Finally, my research focuses on the development and application of a novel
radiochromic gel dosimeter composed of polyvinyl alcohol (PVA), glutaraldehyde (GTA), andpotassium iodide (KI), also known as the PVA-GTA-I gel dosimeter. Gel dosimeters are
chemical-based dosimeters composed of tissue-equivalent materials that allow 3D dose
distribution analysis due to its unique characteristic of recording spatial dose information
within its medium. Measurement and evaluation of gel dosimeters are conducted using
imaging techniques such as spectrophotometry, magnetic resonance imaging (MRI), andoptical computed tomography (OCT). In the PVA-GTA-I gel dosimeter, the radiation-induced
oxidation converts its initial clear and colorless state to red after exposure to ionizing
radiation. Our previous results have highlighted the features of the PVA-GTA-I gel dosimeter,
which are advantageous in radiotherapy dosimetry, such as high sensitivity and potential
reusability through annealing. The characteristics of gel dosimeters are recognized to be
helpful in clinical dosimetry applications[3]. In the context of radiation disaster recovery, geldosimeters have the potential to be utilized as a tool for risk communication. Since the PVAGTA-I gel dosimeter can be molded into anthropomorphic containers and retain the dose
information within its matrix after irradiation, it will be an effective device to visualize how
ionizing radiation is distributed to the human body that the general public could easily
understand. The recent progress and developments of my research in PVA-GTA-I gel
dosimeter are presented in the summary below.
References:[1] Y. Onda et al., “Radionuclides from the Fukushima Daiichi Nuclear Power Plant interrestrial systems,” Nat. Rev. Earth Environ., vol. 1, no. 12, pp. 644–660, 2020, doi:
10.1038/s43017-020-0099-x.
[2] Y. Sun and T. Yan, “The use of public health indicators to assess individual happiness inpost-disaster recovery,” Int. J. Environ. Res. Public Health, vol. 16, no. 21, pp. 1–14, 2019,
doi: 10.3390/ijerph16214101.
[3] G. S. Ibbott, “Applications of gel dosimetry,” J. Phys. Conf. Ser., vol. 3, pp. 58–77, 2004,
doi: 10.1088/1742-6596/3/1/007.

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oTitle of Doctoral ThesisoSummary of Doctoral Thesis

Effect of the glucono-δ-lactone concentration on the sensitivity and stability of PVA-GTA-I
radiochromic gel dosimeter

1. INTRODUCTION
The current and emerging techniques in radiation therapy are becoming more
complex, and the quality assurance of these procedures requires more accurate methods toquantify ionizing radiation fields in three dimensions (3D). Conventional dosimetry systems
such as ionization chambers and radiosensitive films are utilized in clinical settings to verify
dose delivery in modern radiotherapy. However, these dosimeters do not meet the ResolutionTime-Accuracy-Precision (RTAP) criteria for 3D dosimetry and are limited to providing pointor two-dimensional (2D) absorbed dose estimates and sporadic 3D information. Accordingly,
such requisite characteristics could be addressed by gel dosimeters which are chemical-based
dosimeters capable of retaining spatial dose distribution of the radiation-induced reactions
within the gel matrix. The 3D dose information in the gel dosimeters can be measured byseveral imaging techniques such as magnetic resonance imaging (MRI), x-ray computed
tomography (CT), and optical computed tomography (OCT). The characteristics of gel
dosimeters are advantageous in radiotherapy conditions where steep dose gradients arepresent (e.g., intensity-modulated radiation therapy (IMRT) and stereotactic radiosurgery(SRS)). Moreover, the materials used in fabricating most gel dosimeters are radiologicallyequivalent to soft tissues, which can be modified depending on the type of application.
Gel dosimeters are categorized depending on their properties and read-out process;these include Fricke gels, polymer gels, and novel radiochromic gels. In more recent years,
there has been considerable interest in developing and improving radiochromic gel
dosimeters due to its promising features and relatively easier method of measurement. The
mechanism of radiochromic gel dosimeters is based on the radiation-induced color change,
which is proportional to the absorbed dose. The color change can be measured using opticaltechniques such as spectroscopy or OCT. One of the varieties of radiochromic gels is Frickegels infused with Xylenol Orange (XO) based on the radiation-induced oxidation of ferrous
sulfate to ferric ions, which can be measured using MRI. Another sort is the micelleradiochromic gel dosimeter utilizing radiosensitive dyes such as Leuco Crystal Violet (LCV)and Leuco Malachite Green (LMG), which were measured using UV-Vis spectrometer and
OCT.
A recently developed radiochromic gel dosimeter composed of polyvinyl alcohol (PVA)iodide (I) complex with gellan (GG) as the gelling agent was reported. This gel dosimeter
converts from colorless to red after irradiation and can be reused by heating. The redcoloration of this gel results from the oxidation of the PVA-Iodide complex caused by theradiolysis of the water molecules. In contrast, the decolorization is attributed to the additive
fructose, which acts as the reducing sugar. The reagent glutaraldehyde (GTA) was utilized
as a crosslinker to the PVA matrix of Fricke-XO gel (FXG) dosimeters in other studies. PVA
is widely used in fabricating gel dosimeters due to its low diffusion coefficient. Additionally,
GTA has been proven as an effective crosslinker to PVA and can further reduce the spatial
diffusion and increase the sensitivity of gel dosimeters.
We developed our system radiochromic gel dosimeter, called the PVA-GTA-I gel
dosimeter, by applying the PVA-GTA matrix to the PVA-I radiochromic gel dosimeter. Ourpresent research focuses on the effect of one of the additives in our formula, which is glucono3

δ-lactone (GDL). GDL is an acidic coagulant commonly used in the food industry, such as inbean curd and cheese production. Because of its inherent binding and non-toxic properties,
GDL is used in this gel dosimeter formula as a proton generator to promote the cross-linking
process further. Therefore, our objective is to investigate the effect of the GDL concentrationon the dose-response and temporal stability of the PVA-GTA-I formula.
2. MATERIALS AND METHODS

2.1. Gel sample production

All gel samples were fabricated with ultrapure water and analytical-grade chemicals.
The base solution is made of PVA (86–90 mol% saponification, partially hydrolyzed) dissolvedin water using a magnetic stirrer at 80°C for 1 hour. Then, other components of potassium
iodide (KI), fructose, GTA, and GDL were poured into the mixture and stirred until ahomogeneous solution was achieved. Six sets of gels were prepared with various GDL
concentrations (i.e. 50, 100, 150, 200, 250, and 300 mM). The gel solutions were poured into
PMMA cuvettes (10 × 10 × 45 mm3), covered with polyethylene (PE) cover, and stored in a
dry heat sterilizer at 45°C for 12 hours to allow gelation. It should be noted that the gel
samples were prepared and heated the day before irradiation. Additionally, the samples werestabilized for approximately 1 hour after annealing at room temperature (~20°C) before
radiation exposure.

2.2.

137Cs irradiation

A Gammacell-40 research irradiator with a low dose rate (i.e., 0.82 Gy/min) 137Cs
sources was used to irradiate the gel samples with doses from 1 to 10 Gy. One sample wasleft unirradiated as the control sample. The gel dosimeters were positioned at the middle ofthe sample holder with the axes of the cuvettes perpendicular to the source.

2.3. Absorbance measurement and analysis

A UV–Vis spectrophotometer was used to measure the optical absorbance at the
wavelength range of 350–800 nm. Ultrapure water was used to calibrate all the absorbancemeasurements. The change of absorbance (ΔAbs.) was then calculated by the difference
between the measured absorbances of the irradiated sample and the unirradiated (control)
sample. Finally, the temporal stability of the gel was evaluated in a seven-day period after
irradiation with time intervals from 2 to 168 hours at a room temperature range of 20–23°C.
3. RESULTS AND DISCUSSION
The physical appearance of the unirradiated PVA-GTA-I gel sample was colorless andtransparent, while the irradiated samples were converted to red. The color intensity of theirradiated PVA-GTA-I gel was observed to be increasing with radiation dose. This effect was
further emphasized in the absorbance spectrum profiles, where the peak absorbance at 482
nm was increasing. The ΔAbs. plots at 482 nm peak showed good linearities (R2 < 0.99) in thedose range of 0–10 Gy from all the sample sets despite the different GDL concentrations. The
sensitivity, defined by the slope of the linear fitting function, increased with higher GDL
concentrations. However, it was also observed that the increment of sensitivity became small
with the GDL concentration and then completely saturated around 250 mM. The highest
sensitivity range from all the sample sets was 3.8–4.0 x10-2 Gy-1. These values areapproximately 3 to 4 times higher than the reported sensitivity of the PVA-I gel and 6 to 9
times higher than the LCV micelle gels. Though, the sensitivity of the PVA-GTA-I gel wasapproximately two times lower than the PVA-GTA-FXG gels. The absorbance-time plot of the4control (0 Gy) samples showed a gradual increase in absorbance with time. This phenomenon
is caused by the auto-oxidation of the iodide ions in the gel. Moreover, it was also seen thathigher GDL concentrations promote the rate of auto-oxidation in the gel formula. The
temporal stability results of the 10 Gy irradiated samples revealed the trends of the ΔAbs.time plots for the varying GDL concentrations. The sample sets with 100 to 300 mM GDL
exhibited a sharp increase of the ΔAbs during the initial 24 hours followed by small
fluctuations up to 168 hours (7 days) post-irradiation. On the other hand, the sample set with
50 mM GDL showed a gradual rate of increase in ΔAbs, which started at 48 hours after
irradiation and then continued to increase up to 168 hours post-irradiation.
4. CONCLUSION
The increasing concentrations of GDL on the dose-response and temporal stability ofa PVA-GTA-I radiochromic gel dosimeter have been investigated. The PVA-GTA-I gel showedlinear dose-response up to 10 Gy with sensitivities 3-9 times higher than other radiochromic
gel dosimeters. The temporal stability data revealed that higher GDL concentrations increase
the auto-oxidation rate of the PVA-GTA-I gel. Overall, the results obtained into our study
have indicated good insights in the properties of the PVA-GTA-I gel dosimeter with respect
to varying GDL concentrations. Subsequently, the PVA-GTA-I gel dosimeter has shown goodpotential in reusability from our pilot study, an advantageous characteristic for clinical 3D
dosimetry applications in radiotherapy. Further research is recommended to uncover moreof its characteristics in terms of its reusability after repeated heating and irradiations, dose
rate dependence, dose fractionation effects, and spatial stability.
This study was published in Radiation Measurements, 134: 106311, 2020.
oOther theses published in academic research journals[1] Taño, J., Hayashi, S., Hirota, S., Gonzales, C., Yasuda, H., 2019. Development of areusable PVA-GTA-I gel dosimeter for 3D radiation dose assessments. J. Phys. Conf. Ser.
1305, 012034. https://doi.org/10.1088/1742-6596/1305/1/012034[2] Gonzales, C.A.B., Yasuda, H., Hirota, S., Miki, K., Saito, A., Taño, J.E., Nagata, Y., 2019.
Investigation of the applicability of the ESR nail dosimetry for assessment of accidental
exposure
inmedicalfacilities.
Radiat.
Meas.
124,
91–97.
https://doi.org/10.1016/j.radmeas.2019.03.015[3] Gonzales, C.A.B., Yasuda, H., Hirota, S., Miki, K., Saito, A., Taño, J.E., Nagata, Y., 2019.
Fingernail dosimetry using electron spin resonance for radiation disaster response. J.
Phys. Conf. Ser. 1248. https://doi.org/10.1088/1742-6596/1248/1/012072[4] Gonzales, C.A.B., Hirota, S., Taño, J.E., Yasuda, H., 2020. Investigation of the doseresponse in multiple irradiated fingernails and the combined effect of drying timetemperature
to
the
ESR
signal.
Radiat.
Meas.
136.
https://doi.org/10.1016/j.radmeas.2020.106337[5] Gonzales, C.A.B., Taño, J.E., Yasuda, H., 2020. An attempt to reduce the background free
radicals in fingernails for monitoring accidental hand exposure of medical workers. Appl.
Sci. 10, 1–12. https://doi.org/10.3390/app10248949

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