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During radiotherapy, some patients owing to the variability in skin sensitivities, may experience adverse skin reactions for doses at which other patients are asymptomatic. Hence, when abnormal symptoms appear on a patient’s skin, the etiology should be verified. Accordingly, a surface dosimeter on the skin can help ascertain whether accurate doses are irradiated. Furthermore, surface doses are measured in the field junction gaps during craniospinal irradiation or during large-area radiotherapy to avoid adverse reactions due to cumulative skin doses from multiple beams. However, the point dose measurement errors of surface dosimeters exceed approximately 10% and have low-positional accuracies because the attachment sites are approximated with the help of the naked eye. Moreover, accurate information on field junction gaps cannot be obtained. Therefore, in clinical practice, a flexible array dosimeter is required as it can measure the dose distribution on the body surface by adapting its shape to the body curvatures. In this study, we implemented a flexible array dosimeter and, based on its constituent materials, evaluated the attenuation rate associated with its use. A polyester (PET) film was used as the underlying substrate. HgI2 and PbI2 photoconductors were used for their good performances in films. Furthermore, the measurement accuracy was verified through comparisons with Monte Carlo simulation outcomes. The resulting PET film had an attenuation rate of 2.22% at a 50-µm thickness. At the minimum material thickness of 25 µm, the attenuation rates for HgI2 and PbI2 were 4.69% and 5.72%, respectively. Further research is needed to fabricate HgI2-based digital skin dosimeters with a thickness under 25 µm. Radiation detection and pixel resolution should be evaluated to accurately confirm the field junction gap.

Fields that use non-destructive testing (NDT) invest significant amounts of time and resources toward building a radioactive source monitoring system, for preventing any potential radiation-related accidents. However, various elements that can cause potential radiation accidents due to silicon-based photodiodes are involved. Therefore, research on new materials that can effectively detect high-energy gamma ray is necessary. This study focused on developing a new dosimeter material for a real-time monitoring system that can detect the location of a radioactive source. It was confirmed that the fabricated HgI2 dosimeters have sufficient reproducibility and dose linearity for gamma rays. Based on these results, the HgI2 dosimeter was verified to satisfy the general requirements of NDT source-monitoring systems. These monitoring systems are expected to be easily operable by workers and prevent potential radiation accidents.

In intracavitary radiotherapy, it is essential to verify the correct location of radiation source among quality control items because an incorrect location will irradiate an unnecessary dose to normal tissues. As a basic study of digital line dosimeters, this study fabricated a unit cell dosimeter based on polycrystalline mercury (II) iodide (HgI2) and compared its performance with a diode. The study result showed that for reproducibility, the relative standard deviation (RSD) was 1.21%, satisfying the RSD evaluation criterion of within 1.5%. Considering linearity, the coefficient of determination R2 showed an excellent result of 0.9997. Regarding the evaluation of distance dependence, it showed a similar trend in general with a difference of 0.035 cm for intensity 50% when compared with the inverse square value. The angular dependence gradually decreased in intensity as the angle increased, showing a difference of up to 25%. This study suggests the applicability of a digital dosimeter for brachytherapy quality control by evaluating the performance of the HgI2 dosimeter. However, to develop it into a quality assurance (QA) dosimeter, correction factor for sensitivity according to angle should be applied. This study on dosimeter for candidate photoconductor materials can be used as basic data in all areas using radiation.

Objective: This study analyzed the correlation between the average segment width (ASW) and gamma passing rate according to the multi-leaf collimator (MLC) position error. Method: To evaluate the changes in the gamma passing rate according to the MLC position error, 21 volumetric modulated arc therapy (VMAT) plans were generated using pelvic lymph node metastatic prostate cancer patient's data which is sensitive to MLC position errors as they involve several long, narrow, irregular fields. The ASW for each VMAT plan was calculated using our own code developed using Visual Basic for Applications (VBA). The gamma passing rate of the VMAT plan according to the MLC position error was evaluated using ArcCHECK (Sun Nuclear, Melbourne, FL, USA) while inducing symmetric MLC position errors in 0.25 mm intervals from −1 mm to +1 mm in the infinity medical linear accelerator (Elekta AB, Stockholm, Sweden). Finally, we examined the correlation between the change in the passing rate ([Formula: see text]) due to the MLC position error and the ASW in VMAT through linear regression analysis using the least squares method. Results: The ASW and [Formula: see text] were found to have a linear correlation according to the MLC position error, and the coefficient of determination was 0.88. For a 1 mm position error of MLC in VMAT, the gamma passing rate improved by approximately 11.9% as the ASW increased by 10 mm. Conclusion: These results are expected to be employed as guidelines to minimize the dose uncertainty due to MLC position error in VMAT.

Generally, electron therapy is applied to tumors on or close to the skin surface. However, this causes a variety of skin-related side effects. To alleviate the risk of these side effects, clinical treatment uses skin dosimeters to verify the therapeutic dose. However, dosimeters suffer from poor accuracy, because their attachment sites are approximated with the help of naked eyes. Therefore, a dosimeter based on a flexible material that can adjust to the contours of the human body is required. In this study, the reproducibility, linearity, dose-rate dependence, and percentage depth ionization (PDI) of PbO and HgO film-based dosimeters are evaluated to explore their potential as large-scale flexible dosimeters. The results demonstrate that both dosimeters deliver impressive reproducibility (within 1.5%) and linearity (≥ 0.9990). The relative standard deviations of the dose-rate dependence of the PbO and HgO dosimeters were 0.94% and 1.16% at 6 MeV, respectively, and 1.08% and 1.25% at 9 MeV, respectively, with the PbO dosimeter outperforming the 1.1% of existing diodes. The PDI analysis of the PbO and HgO dosimeters returned values of 0.014 cm (–0.074 cm) and 0.051 cm (–0.016 cm), respectively at 6 MeV (9 MeV) compared to the thimble chamber and R50. Therefore, the maximum error of each dosimeter is within the allowable range of 0.1 cm. In short, the analysis reveals that the PbO dosimeter delivers a superior performance relative to its HgO counterpart and has strong potential for use as a surface dosimeter. Thus, flexible monoxide materials have the necessary qualities to be used for dosimeters that meet the requisite quality assurance standards and can satisfy a variety of radiation-related applications as flexible functional materials.

Radiation therapy uses high-energy radiation that can cause various side effects depending on the patient's exposure. In particular, side effects occur in the skin due to its radiation exposure to reach the target volume. Therefore, side effects are reduced by clinical trials using various skin dosimeters such as films and glass detectors to determine the dose exposed to the skin. However, accurately measuring the doses using these dosimeters is challenging due to human curvature. In this study, a flexible skin dosimeter was produced using the photoconductor materials mercury oxide (HgO) and lead oxide (PbO). The performance of the proposed dosimeter was evaluated by measuring reproducibility, linearity, dose rate independency according to dose, and percent depth dose (PDD) at photon energy beam. The results showed that the flexible skin dosimeter using HgO material has high applicability as a skin dosimeter due to its stability compared to PbO. The results provide useful insights for the radiation therapy field, particularly in areas where radiation measurement is difficult, depending on the human curvature. The proposed flexible skin dosimeter could serve in various radiation detection areas as a flexible, functional material

The source position of irradiation is identified using a method that uses rulers and films for quality assurance (QA) in brachytherapy. However, this method involves a high probability of errors, because the scales are checked using the naked eye, and QA is indirectly performed using photographs. Lead monoxide (PbO) is widely used as a semiconductor dosimeter, because it is a photoconductor that generates electrons in response to electromagnetic waves. Moreover, PbO has excellent sensitivity to reflected rays, owing to its high atomic number (Z Pb: 82, Z O: 8) and density (ρPbO: 9.53 g/cm3). We applied PbO to a dosimeter for QA in a brachytherapy device and attempted to increase the signal stability with a parylene coating for performance improvement. Subsequently, a comparative analysis was performed with a PbO dosimeter that was not coated with parylene to determine whether the fabricated dosimeter is applicable as a dosimeter for QA of the brachytherapy device, by analyzing the reproducibility, linearity, percentage interval distance (PID), and angular dependence in the 192Ir source used for brachytherapy. The RSD of the non-parylene PbO dosimeter was 0.85%, and the RSD of the parylene PbO dosimeter was 0.40% in the reproducibility results. In the linearity evaluation results, the R 2 value of the non-parylene PbO dosimeter was 0.9996, and that of the parylene PbO dosimeter was 0.9997 In the PID evaluation results, the difference in the intensity distribution measured according to the distance due to the dose was attenuated at the coated parylene in the case of the parylene PbO dosimeter. Therefore, adjustments using correction coefficients are required for suitable performance. In the angular dependence evaluation results, the parylene PbO dosimeter had 3.44% less angular dependence than the non-parylene dosimeter at an angle of 45°. The parylene-coated PbO dosimeter showed better performance than the non-parylene-coated PbO dosimeter in terms of the reproducibility, linearity, and angular dependence. Therefore, it is considered that the parylene-coated PbO dosimeter can be implemented for QA of brachytherapy devices.

Brachytherapy is a cancer treatment that involves intensively irradiating a tumor by placing a sealed radioactive isotope inside the body. Determining the position of the source through accurate quality assurance (QA) is important, because brachytherapy uses radioactive isotope sources with high dose rates. However, in clinical practice, the source position is determined with the naked eye through the use of a ruler, autoradiograph, video monitor, etc., which yields inaccurate results. Therefore, in this study, a lead (II) iodide (PbI2) based polycrystalline digital dosimeter that can measure the relative dose was developed for the QA of the brachytherapy device, and its applicability was evaluated in terms of reproducibility, linearity, percentage interval distance (PID), and angular dependence. Reproducibility evaluation yielded a relative standard deviation value of 1.41%, which satisfied the evaluation criterion of 1.5%. The linearity evaluation yielded an R2 value of 0.9993, which satisfied the evaluation criterion of 0.9990. The PID evaluation revealed that, as the distance from the source increased, the signal decreased according to the inverse-square law. When the PbI2-based digital dosimeter was rotated up to 45°, a difference of up to 13.20% in the angular dependence was observed. Thus, the dosimeter fabricated in this experiment met all the criteria of the aforementioned evaluations. Therefore, it is considered to be highly applicable as a dosimeter for the QA of brachytherapy devices.

Currently, in the radiation diagnosis field, mammography is used for the early detection of breast cancer. In addition, studies are being conducted on a grid to produce high-quality images. Although the grid ratio of the grid, which affects the scattering removal rate, must be increased to improve image quality, it increases the total exposure dose. While the use of automatic exposure control is recommended to minimize this problem, existing mammography equipment, unlike general radiography equipment, is mounted on the back of a detector. Therefore, the device is greatly affected by the detector and supporting device, and it is difficult to control the exposure dose. Accordingly, in this research, an integrated AEC-grid device that simultaneously performs AEC and grid functions was used to minimize the unnecessary exposure dose while removing scattering, thereby realizing superior image quality.

In radiotherapy, point doses via surface dose measurement are confirmed using a dosimeter attached to the patient's skin. This results in an error margin of about 11.8% or higher because the attachment site is visually confirmed. Thus, a digital flexible array dosimeter that can analyse body surface area is needed. Here, a lead (II) iodide (PbI2)-based unit cell flexible dosimeter was developed, and its electrical properties were evaluated based on its mechanical flexibility by assessing its reproducibility and linearity for bending. The relative standard deviation (RSD) for measurement by the sensor over 10,000 cycles was 1.74% and 2.21% at 6 MV and 15 MV, respectively, which is higher than RSD's evaluation criterion ( 0.9990, the sensitivity at 15 MV was lower than that at 6 MV. The results of this study confirm the applicability and usefulness of the PbI2-based flexible dosimeter in radiation measurements.

Purpose Some recent studies on bendable sensors have reported the reduction of distortion in X-ray shots caused by the patient’s physical structure. In the field of diagnostic radiology, images are nowadays captured using flat panel detectors, but it is difficult to take the geometrical body type and physical characteristics of patients into consideration with flat panels; this may distort images. This study evaluates the bending and electrical properties of bottom electrode-based sensors with bending capability.

Digital radiography is divided into the direct method using photoconductor and indirect method using phosphor based on the principles in acquiring the image information, but both have different advantages and disadvantages. Therefore, this study conducted a preliminary research on the structure of the hybrid detector that combined phosphor and photoconductor to improve the sensitivity of X-ray. As a result, when the tube voltage was adjusted at 30ms of exposure time, the direct structure displayed an overall excellent sensitivity, but at the exposure time of 50ms or more, the hybrid structure displayed a better outcome. This seems to have enough research value considering that various clinical examinations usually include 50ms or more exposure time. Keywords : Digital radiation detector, Structural design, Hybrid, Photoconductor layer, Phosphor layer 요 약 디지털 방사선촬영 기술은 영상 정보를 획득하는 원리에 따라 광도전체를 이용하는 직접 방식과 형광체를 이용하는 간접 방식으로 구분되지만, 모두 다양한 장단점을 내포하고 있다. 이에 본 연구에서는 X-ray 민감도를 개선하고자 형광체 및 광도전체를 병용한 Hybrid 형 검출기의 구조에 대한 기초 연구를 수행하였다. 실험 결과, 조사 시간을 30 ms로 고정하고 관전압을 변화할 경우 전체적으로 직접 방식의 구조에서 우수한 민감도가 나타났으나, 조사 시간이 50 ms 이상에서는 Hybrid 구조의 경우가 더 우수한 것으로 나타났다. 이는 임상에서 다양한 검사를 수행할 경우에 일반적으로 50 ms 이상의 조사시간을 이용한다는 점에서 충분한 연구적 가치를 가질 것으로 사료된다.

To improve the image quality in cone-beam computerized tomography, a detector containing an insulator layer made of parylene-C was utilized in this study. In HgI2 sensors with photoconducting materials, we analyzed the signal based on the thickness of the parylene-C layer and leakage current. In addition, we tried to evaluate the reproducibility of Hgl2 that decreases gradually based on the continuous X-ray study. For the signal-to-noise ratio, we evaluated the photocurrent/darkcurrent (P/D) ratio according to the reduction in the leakage current. Our results indicated a detector reproducibility of 0.82% for a parylene-layer thickness of 18 μm, which represents an improvement of 0.43% over that of a "parylene-free" detector. Compared with the parylene-free sensors, the ones with a parylene layer displayed an approximately linear increase of the P/D ratio with increasing parylene layer thickness. For layers 18 or 20 μm thick this ratio, indicative of image quality, exhibited an improvement of ~ 70 times or more in comparison to a parylene-free sensor.

Recently, cancer has been treated using high dose rates (HDRs), which requires highly reliable treatment plans. In current clinical practice, phosphors are widely used. However, these are of limited use for real-time verification of radiation during HDR brachytherapy; moreover, there is a possibility of electrical error via high-energy radiation because a photodiode is used to detect visible light. Therefore, it is necessary to develop a new dosimeter that can detect gamma rays effectively. This study aimed to investigate the feasibility of a lead monoxide- (PbO)-based dosimeter to detect the position of a radioactive source in HDR brachytherapy. It was confirmed that the fabricated PbO dosimeter has sufficient response coincidence, reproducibility, and dose linearity for gamma rays. Based on these results, it is demonstrated that the PbO dosimeter complies with the general requirements of HDR brachytherapy monitoring systems. Thus, the PbO dosimeter is expected to be used commercially in the future.

In the application of radiotherapy to the skin, the need for ensuring the accuracy of surface dose measurements has attracted increasing attention because dose accumulation and inaccurate skin registration during irradiation can compromise patient safety. Here, we develop a dosimeter with mechanical stability against bending by mixing a photoconductive material, HgI2, and silicon rubber binder. We fabricate a film-type unit cell dosimeter and evaluate the device performance in terms of reproducibility and linearity. We also fabricate a flexible array dosimeter to demonstrate the feasibility of accurate surface dose measurements. To evaluate the robustness of the proposed device to bending, an acrylic filter is applied to form a beam, and the signals measured on flat and curved substrates are compared. The reproducibility values of the film-type unit cell dosimeter are 0.6% (SE) at 6 MV and 1.4% (SE) at 15 MV. The linearity values are 0.9999 (R2) at 6 MV and 0.9981 (R2) at 15 MV. The surface dose measurement error rates are 11.073% at 6 MV and 3.318% at 15 MV, demonstrating the feasibility of the flexible array dosimeter.

Recently, high-energy radiation has been widely used in various industrial fields, including the medical industry, and increasing research efforts have been devoted to the development of radiation detectors to be used with high-energy radiation. In particular, nondestructive industrial applications use high-energy radiation for ships and multilayered objects for accurate inspection. Therefore, it is crucial to verify the accuracy of radiation dose measurements and evaluate the precision and reproducibility of the radiation output dose. Representative detectors currently used for detecting the dose in high-energy regions include Si diodes, diamond diodes, and ionization chambers. However, the process of preparing these detectors is complex in addition to the processes of conducting dosimetric measurements, analysis, and evaluation. Furthermore, the minimum size that can be prepared for a detector is limited. In the present study, the disadvantages of original detectors are compensated by the development of a detector made of a mixture of polycrystalline PbI2 and PbO powder, which are both excellent semiconducting materials suitable for detecting high-energy gamma rays and X-rays. The proposed detector shows characteristics of excellent reproducibility and stable signal detection in response to the changes in energy, and was analyzed for its applicability. Moreover, the detector was prepared through a simple process of particle-in-binder to gain control over the thickness and meet the specific value designated by the user. A mixture mass ratio with the highest reproducibility was determined through reproducibility testing with respect to changes in the photon energy. The proposed detector was evaluated for its detection response characteristics with respect to high-energy photon beam, in terms of dose-rate dependence, sensitivity, and linearity evaluation. In the reproducibility assessment, the detector made with 15 wt% PbO powder showed the best characteristics of 0.59% and 0.25% at 6 and 15 MV, respectively. Based on its selection in the reproducibility assessment, the 15 wt% PbO detector showed no dependence on the dose-rate changes, with R-SD < 1%. Finally, a coefficient of determination of 1 in the linearity assessment demonstrated very good linearity with regards to changes in dose. These results demonstrate the applicability and usefulness of the proposed detector made from a mixture of PbI2 and PbO semiconductors.

With the recent market entries of new types of linear accelerators (LINACs) with a multi leaf collimator (MLC) mounted on them, high-precision radiosurgery applying a LINAC to measure high-dose radiation on the target region has been gaining popularity. Systematic and accurate quality assurance (QA) is of vital important for high-precision radiosurgery because of its increased risk of side effects including life-threatening ones such as overexposure of healthy tissues to high-dose radiation beams concentrated on small areas. Therefore, accurate dose and dose-distribution measurements are crucial in the treatment procedure. The accurate measurement of the properties of beams concentrated on small areas requires high-precision dosimeters capable of high-resolution output and dose mapping as well as accurate dosimetry in penumbra regions. In general, the properties of beams concentrated on small areas are measured using thermos luminescent dosimeters (TLD), diode detectors, ion chambers, diamond detectors, or films, and many papers have presented the advantages and disadvantages of each of these detectors for dosimetry. In this study, a solid-state photoconductor dosimeter was developed, and its clinical usability was tested by comparing its relative dosimetric performance with that of a conventional ion chamber. As materials best-suited for radiation dosimeters, four candidates namely lead (II) iodide (PbI2), lead (II) oxide (PbO), mercury (II) iodide (HgI2), and HgI2/ titanium dioxide (TiO2) composite, the performances of which were proved in previous studies, were used. The electrical properties of each candidate material were examined using the sedimentation method, one of the particle-in-binder (PIB) methods, and unit-cell-type prototypes were fabricated. The unit-cell samples thus prepared were cut into specimens of area 1 × 1 cm2 with 400-μ m thickness. The electrical properties of each sample, such as sensitivity, dark current, output current, rising time, falling time, and response delay, were then measured, in addition to the consistency, reproducibility and linearity of each unit-cell. According to the measurement results, HgI2/TiO2 composite outperformed the other candidate materials. A radiation dosimeter with a chamber-type structure was fabricated in this study using a LINAC under accelerating voltages of 6, and 15 MV and compared with a commercial ion chamber. Percent depth dose (PDD) and beam profile were measured on a water phantom at a fixed area of 10 × 10 cm2 by using the fabricated chamber-type dosimeter, and the values were compared with those measured by a commercial ion chamber. Additionally, a homogeneous phantom was fabricated, and the exposure doses of the center points were measured according to a real treatment plan, followed by a comparison of the measured values as relative values. In this paper, we report that the manufactured dosimeter shows similar characteristics in terms of PDD and beam profile and results for the conventional ion chamber. Based on these results, it is demonstrated that the HgI2/TiO2-based dosimeter complies with radiotherapy QA requirements, namely Superior detection characteristics, consistency, dose linearity, reproducibility. Thus, we expect the HgI2/TiO2-based dosimeter to be used commercially in the future.

In radiation therapy, accurate radiotherapy treatment plan (RTP) reproduction is necessary to optimize the clinical results. Thus, attempts have recently been made to ensure high RTP reproducibility using image-guide radiation therapy (IGRT) technology. However, the clinical use of digital X-ray equipment requires extended quality assurance (QA) for those devices, since the IGRT device quality determines the precision of intensity-modulated radiation therapy. The study described in this paper was focused on developing a multi-energy PbO dosimeter for IGRT device QA. The Schottky-type polycrystalline PbO dosimeter with a Au/PbO/ITO structure was evaluated by comparing its response coincidence, dose linearity, measurement reproducibility, linear attenuation coefficient, and percent depth dose with those of Si diode and standard ionization chamber dosimeters.

Lately, cancer has been treated using high-energy radiation, and this requires highly reliable treatment plans. Therefore, a dosimeter with excellent performance, which is capable of precise dose measurement, is critical. In current clinical practices, an ionization chamber and diode utilizing the ionization reaction mechanism are widely used. Several studies have been carried out to determine optimal materials for the detector in a dosimeter to enable diagnostic imaging. Recently, studies with lead monoxide, which was shown to have low drift current and high resolving power at a high bias, were reported with the dosimeter exhibiting a fast response time against incident photons. This research aims to investigate the feasibility of a lead monoxide-based dosimeter for QA (quality assurance) in radiotherapy. In this paper, we report that the manufactured dosimeter shows similar linearity to a silicon diode and demonstrates similar characteristics in terms of PDD (percent depth dose) results for the thimble ionization chamber. Based on these results, it is demonstrated that the lead monoxide-based dosimeter complies with radiotherapy QA requirements, namely rapid response time, dose linearity, dose rate independence. Thus, we expect the lead monoxide-based dosimeter to be used commercially in the future.

For quality assurance in radiation therapy, several types of dosimeters are used such as ionization chambers, radiographic films, thermo-luminescent dosimeter (TLD), and semiconductor dosimeters. Among them, semiconductor dosimeters are particularly useful for in vivo dosimeters or high dose gradient area such as the penumbra region because they are more sensitive and smaller in size compared to typical dosimeters. In this study, we developed and evaluated Cadmium Telluride (CdTe) dosimeters, one of the most promising semiconductor dosimeters due to their high quantum efficiency and charge collection efficiency. Such CdTe dosimeters include single crystal form and polycrystalline form depending upon the fabrication process. Both types of CdTe dosimeters are commercially available, but only the polycrystalline form is suitable for radiation dosimeters, since it is less affected by volumetric effect and energy dependence. To develop and evaluate polycrystalline CdTe dosimeters, polycrystalline CdTe films were prepared by thermal evaporation. After that, CdTeO3 layer, thin oxide layer, was deposited on top of the CdTe film by RF sputtering to improve charge carrier transport properties and to reduce leakage current. Also, the CdTeO3 layer which acts as a passivation layer help the dosimeter to reduce their sensitivity changes with repeated use due to radiation damage. Finally, the top and bottom electrodes, In/Ti and Pt, were used to have Schottky contact. Subsequently, the electrical properties under high energy photon beams from linear accelerator (LINAC), such as response coincidence, dose linearity, dose rate dependence, reproducibility, and percentage depth dose, were measured to evaluate polycrystalline CdTe dosimeters. In addition, we compared the experimental data of the dosimeter fabricated in this study with those of the silicon diode dosimeter and Thimble ionization chamber which widely used in routine dosimetry system and dose measurements for radiation therapy.