• Journal of Radiation Protection and Research
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• v.40 no.4
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• pp.194-201
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• 2015

We have investigated the EPR signal properties in 12 components of two mobile phones (LCD, OLED) using electron paramagnetic resonance (EPR) spectrometer in this study.EPR measurements were performed at normal atmospheric conditions using Bruker EXEXSYS-II E500 spectrometer with X-band bridge, and samples were irradiated by $^{137}Cs$ gamma-ray source. To identify the presence of radiation-induced signal (RIS), the EPR spectra of each sample were measured unirradiated and irradiated at 50 Gy. Then, dose-response curve and signal intensity variating by time after irradiation were measured. As a result, the signal intensity increased after irradiation in all samples except the USIM plastic and IC chip. Among the samples, cover glass(CG), lens, light guide plate(LGP) and diffusion sheet have shown fine linearity ($R^2$ > 0.99). Especially, the LGP had ideal characteristics for dosimetry because there were no signal in 0 Gy and high rate of increase in RIS. However, this sample showed weakness in fading. Signal intensity of LGP and Diffusion Sheet decreased by 50% within 72 hours after irradiation, while signals of Cover Glass and Lens were stably preserved during the short period of time. In order to apply rapidly EPR dosimetry using mobile phone components in large-scale radiation accidents, further studies on signal differences for same components of the different mobile phone, fading, pretreatment of samples and processing of background signal are needed. However, it will be possible to do dosimetry by dose-additive method or comparative method using unirradiated same product in small-scale accident.

• The Journal of Korean Society for Radiation Therapy
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• v.16 no.2
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• pp.43-61
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• 2004

Purpose : For qualify improvement in radiotherapy, it is important to set up and evaluate equipment (linac) accurately. In addition, technicians are needed to be fully aware of the equipment's detailed quality and its manual. Therefore, the result of ATP is evaluated and introduced, in order that the technicians are skilled by participating in quality assurance (QA) and understanding the quality of the equipment before clinical use. Method and Material : QA for LINAC 21EX (Varian, US) was done with suppliers its procedure was divided into radiation survey, mechanical test, radiation isocenter test, bean performance, dosimetry, and enhanced dynamic wedge and using X-omat film (Kodak), multidata, densitometer, and electrometer. QA of MLC (Millennium, 120 leaf) attached to LINAC and EPID (Portal vision) were done separately. Result : The leakage dose by survey meter was below the tolerance. In mechanical test, collimater, gantry, and couch rotation were less than 1mm, and the angles were ${\pm}0.1^{\circ}$ for digital and ${\pm}0.5^{\circ}$ for mechanical. The alignment test of the light field and crosshair were evaluated less than 1mm. The (a)symmetrical jaw field was less than ${\pm}0.5mm$. The radiation isocenter test using X-mat film was less than 1mm. The consistency of light field and radiation field was less than ${\pm}0.1mm$. PDD for photon energy was less than ${\pm}1\%$ and for electron energy of $90\%,\;80\%,\;50\%,\;and\;30\%$ were evaluated within the tolerance. Flatness for photon and electron energy was evaluated $2.3\%$ (tolerance $3\%$) and $3\%$ (tolerance $4.5\%$), respectively, and symmetry was $0.45\%$ (tolerance $2\%$) and $0.3\%$ (tolerance $2\%$), respectively. Dosimetry test for short term, MU setting, rep rate, and dose rate accuracy of photon and electron energy was within the tolerance depending on energy, MU, and gantry angle. Conclusion : Accuracy and safety for clinical use of Clinac 21EX was verified through customer acceptance procedure and the quality of the equipment was found out. These can reduce the difficulties in using the equipment. Furthermore, it is useful for clinically treatment of patients by technicians' active participations.

• Nuclear Engineering and Technology
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• v.54 no.1
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• pp.255-261
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• 2022

A reliable and well-characterized dosimetry system which is traceable to the international measurement system, is the key element to quality assurance in radiation processing with cobalt-60 gamma rays, X-rays, and electron beam. This is specifically the case for health-regulated processes, such as the radiation sterilization of single use medical devices and food irradiation for preservation and disinfestation. Polyethylene is considered to possess a lot of interesting dosimetric characteristics. In this work, a detailed study has been performed to determine the dosimetric characteristics of a commercialized high-density polyethylene (HDPE) film using Fourier transformed infrared spectrometry (FTIR). Correlations have been established between the absorbed dose and radiation induced infrared absorption in polyethylene having a maximum at 965 cm^-1 (transvinylene band) and 1716 cm^-1 (ketone-carbonyl band). We have found that polyethylene dose-response is linear with dose for both bands up to1000 kGy. For transvinylene band, the dose-response is more sensitive if irradiations are made in helium. While, for ketone-carbonyl band, the dose-response is more sensitive when irradiations are carried out in air. The dose-rate effect has been found to be negligible when polyethylene samples are irradiated with electron beam high dose rates. The irradiated polyethylene is relatively stable for several weeks after irradiation.

• Progress in Medical Physics
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• v.11 no.2
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• pp.91-99
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• 2000

This is a preliminary study for developing the method of the dose reconstruction in the patients, irradiated by mega-voltage photon beams from the linear accelerator, using the transit dose distributions. In this study we present the method of three-dimensional dose reconstruction and evaluate the method by computer simulation. To acquire the dose distributions in the patients (or phantoms) we first calculate the differences between the doses at the arbitrary points in the patients and the doses at the corresponding points where the transit doses are measured. Then, we can get the dose in the patients from the measured transit dose and the calculated value of the difference. The dose differences are calculated by applying the inverse square law and using the linear attenuation coefficient. The scatter to primary dose ratios, which are calculated by the Monte Carlo program using the CT data of the patient (or phantoms), are also used in the calculations. For the evaluation of this method we used various kinds of homogeneous and inhomogeneous phantoms and calculated the transit dose distributions with the Monte Carlo program. From the distributions we reconstructed the dose distributions in the phantom. We used mono-energy Photon beam of 1.5MeV and Monte Carlo program EGS4. The comparison between the dose distributions reconstructed using the method and the distributions calculated by the Monte Carlo program was done. They agreed within errors of -4%∼+2%. This method can be used to predict the dose distributions in the patient

• Proceedings of the Korean Society of Medical Physics Conference
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• 2004.11a
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• pp.153-156
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• 2004

Korea Food and Drug Administration(KFDA) has peformed the calibration of therapy level dosimeters for Co-60 radiation since 1979. The reference standard ionization chamber has been calibrated at BIPM in France. The uncertainty on the KFDA calibration coefficients is 0.9 %(k=2) for air kerma and absorbed dose to water. Since 1999 a national quality audit program for ensuring dosimetry accuracy in Korea radiotherapy centers has been performed by the KFDA. The uncertainty associated with the determination of the absorbed dose to water from the TLD readings for high energy x-ray is 1.6 %(k=1). The correction factors for energy, non-linearity dose response, and TLD holder are used in the dose determination. Agreement between the user stated dose and KFDA measured dose within ${\pm}$ 5 % is considered acceptable. KFDA TLD postal dose quality audit program was peformed for 71 beam qualities of 53 domestic radiotherapy centers in 2003. The results for quality assurance showed that 63 out of 71 beam qualifies (89 %) satisfied the acceptance limit. The second audit was carried out for the centers outside the limit and ail of them have been corrected.

• Radiation Oncology Journal
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• v.22 no.1
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• pp.64-68
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• 2004

Purpose : To study the feasibility of verifying real-time 2-D dose distribution measurement system with the scintillation screen for the quality assurance. Materials and Methods : The water phantom consisted of a scintillation screen (LANEX fast screen, Kodak, USA) that was axially located in the middle of an acrylic cylinder with a diameter of 25 cm. The charge-coupled device (CCD) camera was attached to the phantom In order to capture the visible light from the scintillation screen. To observe the dose distribution In real time, the intensity of the light from the scintillator was converted to a dosage. The isodose contours of the calculations from RTP and those of the measurements using the scintillation screen were compared for the arc therapy and the Intensity modulated radiation therapy (IMRT). Results : The kernel, expressed as a multiplication of two error functions, was obtained in order to correct the sensitivity of the CCD of the camera and the scintillation screen. When comparing the calculated isodose and measured isodose, a discrepancy of less than 8 mm in the high dose region was observed. Conclusion : Using the 2-D dosimetry system, the relationship between the light and the dosage could be found, and real-time verification of the dose distribution was feasible.

• Progress in Medical Physics
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• v.23 no.2
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• pp.123-126
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• 2012

For the purpose of quality assurance (QA) of the blood irradiator, QA programs for daily, monthly, and yearly were developed. For daily tests, simple items for basically operating the machine are recommended. For monthly and yearly tests, the measurement of dose to assure the dose delivery system are performed by a dosimetry devices (Glass dosimeter jig) developed in this study. The QA program is practical for clinical environment.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2004.11a
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• pp.166-169
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• 2004

In the International Code of Practice for dosimetry TRS-398 published by International Atomic Energy Agency(IAEA), water equivalency plastic phantom may be used under certain circumstances for electron beam dosimetry for beam quality E0${\leq}$ 10 MeV. In this study, Palstic Water$^{TM}$ and Virtual Water$^{TM}$ were evaluated in order to determine fluence scaling factor hpl. Plastic phantom was evaluated for five electron energy from 6 MeV to 20 MeV. From the measured data of Palstic Water$^{TM}$, the fluence scaling factor hpl was found to be average 0.9964 and Virtual Water$^{TM}$ fluence scaling factor was 1.0156.

• Progress in Medical Physics
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• v.7 no.2
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• pp.57-65
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• 1996

Total Skin Electron Beam Therapy (TSEBT) is one of the most effective treatment methods for superficially disseminated skin cancer or cutaneous T-cell lymphoma. We have treated a patient with cutaneous T-cell lymphoma. We have used Stanford technique using six dual field. The nominal energy of electron beam was 4MeV. SSD was 390cm and the gantry angles of dual fields were 76$^{\circ}$ and 104$^{\circ}$. The dose profiles of single field and dual fields were measured with films and a Farmer type ion chamber. The field uniformity was 10％ over the patient's surface. During treatment, the patient was placed in six different positions for homogenous dose distribution over the body surface. The areas not directly exposed to the path of the electron beam (soles of feet, perineum and vertex of scalp) were boosted with 7MeV electron beam. During the treatment, lens, fingernails and toenails were shielded.

• Progress in Medical Physics
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• v.28 no.2
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• pp.54-60
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• 2017

This study was designed to measure transit dose with an electronic portal imaging device (EPID) in eight patients treated with intensity modulated radiotherapy (IMRT), and to verify the accuracy of dose delivery to patients. The calculated dose map of the treatment planning system (TPS) was compared with the EPID based dose measured on the same plane with a gamma index method. The plan for each patient was verified prior to treatment with a diode array (MapCHECK) and portal dose image prediction (PDIP). To simulate possible patient positioning errors during treatment, outcomes were evaluated after an anthropomorphic phantom was displaced 5 and 10 mm in various directions. Based on 3%/3 mm criteria, the $mean{\pm}SD$ passing rates of MapCHECK, PDIP (pre-treatment QA) for 47 IMRT were $99.8{\pm}0.1%$, $99.0{\pm}0.7%$, and, respectively. Besides, passing rates using transit dosimetry was $90.0{\pm}1.5%$ for the same condition. Setup errors of 5 and 10 mm reduced the mean passing rates by 1.3% and 3.0% (inferior to superior), 2.2% and 4.3% (superior to inferior), 5.9% and 10.9% (left to right), and 8.9% and 16.3% (right to left), respectively. These findings suggest that the transit dose-based IMRT verification method using EPID, in which the transit dose from patients is compared with the dose map calculated from the TPS, may be useful in verifying various errors including setup and/or patient positioning error, inhomogeneity and target motions.