• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.115-116
• /
• 2012

The demand for flexible electronic systems such as wearable computers, E-paper, and flexible displays has increased due to their advantages of excellent portability, conformal contact with curved surfaces, light weight, and human friendly interfaces over present rigid electronic systems. This seminar introduces three recent progresses that can extend the application of high performance flexible inorganic electronics. The first part of this seminar will introduce a RRAM with a one transistor-one memristor (1T-1M) arrays on flexible substrates. Flexible memory is an essential part of electronics for data processing, storage, and radio frequency (RF) communication and thus a key element to realize such flexible electronic systems. Although several emerging memory technologies, including resistive switching memory, have been proposed, the cell-to-cell interference issue has to be overcome for flexible and high performance nonvolatile memory applications. The cell-to-cell interference between neighbouring memory cells occurs due to leakage current paths through adjacent low resistance state cells and induces not only unnecessary power consumption but also a misreading problem, a fatal obstacle in memory operation. To fabricate a fully functional flexible memory and prevent these unwanted effects, we integrated high performance flexible single crystal silicon transistors with an amorphous titanium oxide (a-TiO2) based memristor to control the logic state of memory. The $8{\times}8$ NOR type 1T-1M RRAM demonstrated the first random access memory operation on flexible substrates by controlling each memory unit cell independently. The second part of the seminar will discuss the flexible GaN LED on LCP substrates for implantable biosensor. Inorganic III-V light emitting diodes (LEDs) have superior characteristics, such as long-term stability, high efficiency, and strong brightness compared to conventional incandescent lamps and OLED. However, due to the brittle property of bulk inorganic semiconductor materials, III-V LED limits its applications in the field of high performance flexible electronics. This seminar introduces the first flexible and implantable GaN LED on plastic substrates that is transferred from bulk GaN on Si substrates. The superb properties of the flexible GaN thin film in terms of its wide band gap and high efficiency enable the dramatic extension of not only consumer electronic applications but also the biosensing scale. The flexible white LEDs are demonstrated for the feasibility of using a white light source for future flexible BLU devices. Finally a water-resist and a biocompatible PTFE-coated flexible LED biosensor can detect PSA at a detection limit of 1 ng/mL. These results show that the nitride-based flexible LED can be used as the future flexible display technology and a type of implantable LED biosensor for a therapy tool. The final part of this seminar will introduce a highly efficient and printable BaTiO3 thin film nanogenerator on plastic substrates. Energy harvesting technologies converting external biomechanical energy sources (such as heart beat, blood flow, muscle stretching and animal movements) into electrical energy is recently a highly demanding issue in the materials science community. Herein, we describe procedure suitable for generating and printing a lead-free microstructured BaTiO3 thin film nanogenerator on plastic substrates to overcome limitations appeared in conventional flexible ferroelectric devices. Flexible BaTiO3 thin film nanogenerator was fabricated and the piezoelectric properties and mechanically stability of ferroelectric devices were characterized. From the results, we demonstrate the highly efficient and stable performance of BaTiO3 thin film nanogenerator.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.53 no.8
• /
• pp.39-48
• /
• 2016

In this paper, we propose thermal resistance compact model of FinFET structure that has hexagon shaped source/drain. The heating effect and thermal properties were increased by reduced size of the device, and thermal resistance is an important factor to analyze the effect and the properties. The heat source and each contact that is moved heat out were set up in transistor, and domain is divided by the heat source and the four parts of contacts : source, drain, gate, substrate. Each contact thermal resistance model is subdivided as a easily interpretable structure by analyzing the temperature and heat flow of the TCAD simulation results. The domains are modeled based on an integration or conformal mapping method through the structure parameters according to its structure. First modeled by analyzing the thermal resistance to a single fin, and applying the change in the parameter of the channel increases to improve the accuracy of the thermal resistance model of the multi-fin/ finger. The proposed thermal resistance model was compared to the thermal resistance by analyzing results of the 3D Technology CAD simulations, and the proposed total thermal resistance model has an error of 3 % less in single and multi-finl. The proposed thermal resistance model can predict the thermal resistance due to the increase of the fin / finger, and the circuit characteristics can be improved by calculating the self-heating effect and thermal characterization.

• Radiation Oncology Journal
• /
• v.34 no.4
• /
• pp.265-272
• /
• 2016

Purpose: The purpose of this study is to evaluate the treatment outcomes of adjuvant radiotherapy using vaginal brachytherapy (VB) with a lower dose per fraction and/or external beam radiotherapy (EBRT) following surgery for patients with stage I endometrial carcinoma. Materials and Methods: The subjects were 43 patients with the International Federation of Gynecology and Obstetrics (FIGO) stage I endometrial cancer who underwent adjuvant radiotherapy following surgery between March 2000 and April 2014. Of these, 25 received postoperative VB alone, while 18 received postoperative EBRT to the whole pelvis; 3 of these were treated with EBRT plus VB. The median EBRT dose was 50.0 Gy (45.0-50.4 Gy) and the VB dose was 24 Gy in 6 fractions. Tumor dose was prescribed at a depth of 5 mm from the cylinder surface and delivered twice per week. Results: The median follow-up period for all patients was 57 months (range, 9 to 188 months). Five-year disease-free survival (DFS) and overall survival (OS) for all patients were 92.5% and 95.3%, respectively. Adjuvant radiotherapy was performed according to risk factors and stage IB, grade 3 and lymphovascular invasion were observed more frequently in the EBRT group. Five-year DFS for EBRT and VB alone were 88.1% and 96.0%, respectively (p = 0.42), and 5-year OS for EBRT and VB alone were 94.4% and 96%, respectively (p = 0.38). There was no locoregional recurrence in any patient. Two patients who received EBRT and 1 patient who received VB alone developed distant metastatic disease. Two patients who received EBRT had severe complications, one each of grade 3 gastrointestinal complication and pelvic bone insufficiency fracture. Conclusion: Adjuvant radiotherapy achieved high DFS and OS with acceptable toxicity in stage I endometrial cancer. VB (with a lower dose per fraction) may be a viable option for selected patients with early-stage endometrial cancer following surgery.

• Radiation Oncology Journal
• /
• v.33 no.4
• /
• pp.276-283
• /
• 2015

Purpose: We evaluated the efficacy and toxicity of repeated high dose 3-dimensional conformal radiation therapy (3D-CRT) for patients with unresectable hepatocellular carcinoma. Materials and Methods: Between 1998 and 2011, 45 patients received hepatic re-irradiation with high dose 3D-CRT in Samsung Medical Center. After excluding two ineligible patients, 43 patients were retrospectively reviewed. RT was delivered with palliative or salvage intent, and equivalent dose of 2 Gy fractions for ${\alpha}/{\beta}=10Gy$ ranged from $31.25Gy_{10}$ to $93.75Gy_{10}$ (median, $44Gy_{10}$). Tumor response and toxicity were evaluated based on the modified Response Evaluation Criteria in Solid Tumors criteria and the Common Terminology Criteria for Adverse Events (CTCAE) ver. 4.0. Results: The median follow-up duration was 11.2 months (range, 4.1 to 58.3 months). An objective tumor response rate was 62.8%. The tumor response rates were 81.0% and 45.5% in patients receiving ${\geq}45Gy_{10}$ and $<45Gy_{10}$, respectively (p = 0.016). The median overall survival (OS) of all patients was 11.2 months. The OS was significantly affected by the Child-Pugh class as 14.2 months vs. 6.1 months (Child-Pugh A vs. B, p < 0.001), and modified Union for International Cancer Control (UICC) T stage as 15.6 months vs. 8.3 months (T1-3 vs. T4, p = 0.004), respectively. Grade III toxicities were developed in two patients, both of whom received ${\geq}50Gy_{10}$. Conclusion: Hepatic re-irradiation may be an effective and tolerable treatment for patients who are not eligible for further local treatment modalities, especially in patients with Child-Pugh A and T1-3.

• Journal of Radiation Protection and Research
• /
• v.28 no.3
• /
• pp.225-231
• /
• 2003

Up-front irradiation technique as 3-dimensional conformation, or intensity modulation has kept large proportion of brain tumors from being complicated with acute radiation reactions in the normal tissue during or shortly after radiotherapy. For years, we've cannot help but counting on 2-D vertex beam technique to reduce acute reactions in the brain tumor patients because we're not equipped with 3-dimensional planning system. We analyzed its advantages and limitations in the clinical application. From 1998 to 2001, vertex or oblique vertex beams were applied to 35 patients with primary brain tumor and 25 among them were eligible for this analysis. Vertex(V) plans were optimized on the reconstructed coronal planes. As the control, we took the bilateral opposed techniques(BL) otherwise being applied. We compared the volumes included in 105% to 50% isodose lines of each plan. We also measured the radiation dose at various extracranial sites with TLD. With vertex techniques, we reduced the irradiated volumes of contralateral hemisphere and prevented middle ear effusion at contralateral side. But the low dose volume increased outside 100%; the ratio of V to BL in irradiated volume included in 100%, 80%, 50% was 0.55+/-0.10, 0.61+/-0.10, and 1.22+/-0.21, respectively. The hot area within 100% isodose line almost disappeared with vertex plan; the ratio of V to BL in irradiated volume included in 103%, 105%, 108% was 0.14+/-0.14, 0.05./-0.17, 0.00, respectively. The dose distribution within 100% isodose line became more homogeneous; the ratio of volume included in 103% and 105% to 100% was 0.62+/-0.14 and 0.26+/-0.16 in BL whereas was 0.16+/-0.16 and 0.02+/-0.04 in V. With the vertex techniques, extracranial dose increased up to $1{\sim}3%$ of maximum dose in the head and neck region except submandibular area where dose ranged 1 to 21%. From this data, vertex beam technique was quite effective in reduction of unnecessary irradiation to the contralateral hemispheres, integral dose, obtaining dose homogeneity in the clinical target. But it was associated with volume increment of low dose area in the brain and irradiation toward the head and neck region otherwise being not irradiated at all. Thus, this 2-D vertex technique can be a useful quasi-conformal method before getting 3-D apparatus.

• Progress in Medical Physics
• /
• v.27 no.1
• /
• pp.37-45
• /
• 2016

In proton therapy, in vivo proton beam range verification is very important to deliver conformal dose to the target volume and minimize unnecessary dose to normal tissue. For this purpose, a multi-slit prompt-gamma camera module made of 24 scintillation detectors and 24-channel signal processing system is under development. In the present study, we have developed and tested a dual-mode signal processing system, which can operate in the energy calibration mode and the fast data acquisition mode, to process the signals from the 24 scintillation detectors. As a result of performance test, using the energy calibration mode, we were able to perform energy calibration for the 24 scintillation detectors at the same time and determine the discrimination levels for the detector channels. Further, using the fast data acquisition mode, we were able to measure a prompt-gamma distribution induced by a 45 MeV proton beam. The measured prompt gamma distribution was found similar to the proton dose distribution at the distal fall-off region, and the estimated beam range was $17.13{\pm}0.76mm$, which is close to the proton beam range of 16.15 mm measured by an EBT film.

• Progress in Medical Physics
• /
• v.14 no.3
• /
• pp.151-160
• /
• 2003

The application of more complex radiotherapy techniques using multileaf collimation (MLC), such as 3D conformal radiation therapy and intensity-modulated radiation therapy (IMRT), has increased the significance of verifying leaf position and motion. Due to thier reliability and empirical robustness, quality assurance (QA) of MLC. However easy use and the ability to provide digital data of electronic portal imaging devices (EPIDs) have attracted attention to portal films as an alternatives to films for routine qualify assurance, despite concerns about their clinical feasibility, efficacy, and the cost to benefit ratio. In this study, we developed method for daily QA of MLC using electronic portal images (EPIs). EPID availability for routine QA was verified by comparing of the portal films, which were simultaneously obtained when radiation was delivered and known prescription input to MLC controller. Specially designed two-test patterns of dynamic MLC were applied for image acquisition. Quantitative off-line analysis using an edge detection algorithm enhanced the verification procedure as well as on-line qualitative visual assessment. In conclusion, the availability of EPI was enough for daily QA of MLC leaf position with the accuracy of portal films.

• Progress in Medical Physics
• /
• v.23 no.3
• /
• pp.127-137
• /
• 2012

A conversing beam is firstly designed for radiosurgery by a neurosugern Lars Leksell in 1949 with orthogonal x-rays tube moving through horizontal moving arc to focusing the beam at target center. After 2 decades he composits 201 source of the Co-60 for gamma knife which beams focused at locus. Sveral linac-based stereotactic radiosurgery using the circular collimated beam which size range for 0.4~4.0 cm in a diameter by non-coplanar multiarc have been developed over the decades. The irregular lesions can be treated by superimposing with several spherical shots of radiation over the tumour volume. Linac based techniques include the use of between 4 and 11 non-co-planar arcs and a dynamic rotation technique and use photon beam energies in the range of 6~10 MV. Reviews of the characteristics of several treatment techniques can be found in the literature (Podgorsak 1989, Schell 1991). More in recent, static conformal beams defined by custom shaped collimators or a mini- or micro-multileaf collimator (mMLC) have been used in SRS. Finally, in the last few years, intensity-modulated mMLC SRS has also been introduced. Today, many commercial and in-house SRS programs have also introduced non-invasive immobilization systems include the cyberknife and tomotherapy and proton beam. This document will be compared the characteristics of dose distribution of radiosurgery as introduced gamma knife, BrainLab include photon knife in-house SRS program and cyberknife in currently wide used for a cranial SRS.

• Progress in Medical Physics
• /
• v.28 no.4
• /
• pp.218-225
• /
• 2017

Effects on skin caused by the dose from linear accelerator (LINAC) opposing portal irradiation and TomoDirect 3-D modeling treatment according to the radiation devices and treatment methods were measured, and a comparative analysis was performed. Two groups of 10 patients each were created and measurements were carried out using an optically stimulated luminescence dosimeter. These patients were already receiving radiation treatment in the hospital. Using the SPSS statistical program, the minimum and maximum average standard deviations of the measured skin dose data were obtained. Two types of treatment method were selected as independent variables; the measured points and total average were the dependent variables. An independent sample T-test was used, and it was checked whether there was a significance probability between the two groups. The average of the measured results for the LINAC opposing portal radiation was 117.7 cGy and PDD 65.39% for the inner breast, 144.7 cGy and PDD 80.39% for the outer breast, 143.2 cGy and PDD 79.56% for the upper breast, 151.4 cGy and PDD 84.11% for the lower breast, 149.6 cGy and PDD 83.11% for the axilla, and 141.32 cGy and PDD 78.51% for the total average. In contrast, for TomoDirect 3-D conformal radiotherapy, the corresponding measurement values were 137.6 cGy and PDD 76.44%, 152.3 cGy and PDD 84.61%, 148.6 cGy and PDD 82.56%, 159.7 cGy and PDD 88.72%, and 148.6 cGy PDD 82.56%, respectively, and the total average was 149.36 cGy and PDD 82.98%. To determine if the difference between the total averages was statistically significant, the independent sample T-test of the SPSS statistical program was used, which indicated that the P-value was P=0.024, which was 0.05 lower than the significance level. Thus, it can be understood that the null hypothesis can be dismissed, and that there was a difference in the averages. In conclusion, even though the treatment dose was similar, there could be a difference in the dose entering the body surface from the radiation treatment plan; however, depending on the properties of the treatment devices, there is a difference in the dose affecting the body surface. Thus, the absorbed dose entering the body surface can be high. During breast cancer radiotherapy, radiation dermatitis occurs in almost all patients. Most patients have a difficult time while undergoing treatment, and therefore, when choosing a radiotherapy treatment method, minimizing radiation dermatitis is an important consideration.

• The Journal of Korean Society for Radiation Therapy
• /
• v.28 no.2
• /
• pp.131-137
• /
• 2016

Purpose : The bladder volume change was measured using ultrasonography for helping decrease the side effects and other organ variations in the location of radiation therapy for cervical cancer patients. An experiment was performed targeting patients who were treated with radiation therapy at PNUH within the period from September to December 2015. Materials and Methods : To maintain the bladder volume, each patient was instructed to drink 500 cc water before and after CT simulation, 60 minutes before the dry run. Also, the bladder volume was measured in each patient CT scan, and a 3D conformal therapy plan was designed. The bladder volumes measured before and after the CT simulation, dry run, and radiation treatment planning were compared and analyzed. Results : The average volume and average error of the bladder that were obtained from the measurement based on the CT scan images had the lowest standard deviation in the CT simulation. This means that the values that were obtained before and after the CT simulation were statistically relevant and correlative. Moreover, the bladder volume measured via ultrasonography was larger size, the average volume in the CT scan. But the values that were obtained Dry run and after the CT simulation were not statistically relevant. Conclusion : Drinking a certain amount of water helps a patient maintain his/her bladder volume for a dry run. Even then, it is difficult to maintain the bladder volume for the dry run. Also, whether or not the patients followed the directions for the dry run correctly is important.