• Journal of Radiation Protection and Research
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• v.44 no.3
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• pp.97-102
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• 2019

Background: Dose rate meters are the most widely used, and perhaps one of the most important tools for the measurement of ionising radiation. They are often the first, or only, device available to a user for an instant check of radiation dose at a certain location. Throughout the world, radiation safety practices rely strongly on the output of these dose rate meters. But how well do we know the quality of their output? Materials and Methods: This review is based on the measurements 1,158 commercially available dose rate meters of 116 different makes and models. Expected versus the displayed dose patterns and consistency was checked at various dose rates between $5{\mu}Gy{\cdot}h^{-1}$ and $2mGy{\cdot}h^{-1}$. Samples of these meters were then selected for further investigation and were exposed to radiation sources covering photon energies from 50 keV to 1.5 MeV. The effect of detector orientation on its reading was also investigated. Rather than focusing on the angular response distribution that is often reported by the manufacturer of the device, this study focussed on the design ergonomics i.e. the angles that the operator will realistically use to measure a dose rate. Results and Discussion: This review shows the scope and boundaries of the ionising radiation dose rate estimations that are made using commonly available meters. Observations showed both inter and intra make and model variations, occasional cases of instrument failure, instrument walk away, and erroneous response. Conclusion: The results indicate the significance of selecting and maintaining suitable monitors for specific applications in radiation safety.

• Progress in Medical Physics
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• v.33 no.4
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• pp.150-157
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• 2022

Purpose: Elekta synergy^® was commissioned in the Seoul National University Veterinary Medical Teaching Hospital. Recently, Chung-Ang University Gwang Myeong Hospital commissioned Elekta Versa HD^TM. The beam characteristics of both machines are similar because of the same Agility^TM MLC Model. We compared measured beam data calculated using the Elekta treatment planning system, Monaco^®, for each institute. Methods: Beam of the commissioning Elekta linear accelerator were measured in two independent institutes. After installing the beam model based on the measured beam data into the Monaco^®, Monte Carlo (MC) simulation data were generated, mimicking the beam data in a virtual water phantom. Measured beam data were compared with the calculated data, and their similarity was quantitatively evaluated by the gamma analysis. Results: We compared the percent depth dose (PDD) and off-axis profiles of 6 MV photon and 6 MeV electron beams with MC calculation. With a 3%/3 mm gamma criterion, the photon PDD and profiles showed 100% gamma passing rates except for one inplane profile at 10 cm depth from VMTH. Gamma analysis of the measured photon beam off-axis profiles between the two institutes showed 100% agreement. The electron beams also indicated 100% agreement in PDD distributions. However, the gamma passing rates of the off-axis profiles were 91%-100% with a 3%/3 mm gamma criterion. Conclusions: The beam and their comparison with MC calculation for each institute showed good performance. Although the measuring tools were orthogonal, no significant difference was found.

• Preventive Nutrition and Food Science
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• v.7 no.2
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• pp.195-200
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• 2002

Changes in accumulated pulsed photostimulated luminescene (PPSL) signals were observed after storage, which affected the ability to detect irradiation in black and white peppers. The PPSL curves were accumulated linearly during the 120 s measurement times, and PPSL signals increased according to irradiation doses. Threshold levels of black and white peppers were below 557$\pm$220 and 503$\pm$92 photon counts in 60 s, and below 679$\pm$351 and 812 $\pm$ 648 photon counts in 120 s, respectively. The PPSL signals of black and white peppers linearly increased with irradiation dose up to 5 kGy, but very little from 5~10 kCy. The accumulated PPSL signals of irradiated black and white peppers had higher decay rates when stored in normal room conditions than in a darkroom Detection of irradiation was possible for up to 12 months after irradiation, if the samples were stored in a darkroom.

• Progress in Medical Physics
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• v.32 no.4
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• pp.145-152
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• 2021

Purpose: During the treatments of cancer patients with a linear accelerator (LINAC) using photon beams with energies ≥8 MV, the components inside the LINAC head get activated through the interaction of photonuclear reaction (γ, n) and neutron capture (n, γ). We used spectroscopy and measured the dose rate for the LINAC in operation after the treatment ended. Methods: We performed spectroscopy and dose rate measurements for three units of LINACs with a portable high-purity Germanium (HPGe) detector and a survey meter. The spectra were obtained after the beams were turned off. Spectroscopy was conducted for 3,600 seconds, and the dose rate was measured three times. We identified the radionuclides for each LINAC. Results: According to gamma spectroscopy results, most of the nuclides were short-lived radionuclides with half-lives of 100 days, except for ⁶⁰Co, ⁶⁵Zn, and ¹⁸¹W nuclides. The dose rate for three LINACs obtained immediately in front of the crosshair was in the range of 0.113 to 0.129 µSv/h. The maximum and minimum dose rates measured on weekends were 0.097 µSv/h and 0.092 µSv/h, respectively. Compared with the differences in weekday data, there was no significant difference between the data measured on Saturday and Sunday. Conclusions: Most of the detected radionuclides had half-lives <100 days, and the dose rate decreased rapidly. For equipment that primarily used energies ≤10 MV, when the equipment was transferred after at least 10 minutes after shutting it down, it is expected that there will be little effect on the workers' exposure.

• Journal of Radiation Protection and Research
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• v.10 no.2
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• pp.155-159
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• 1985

In general, dose rates for a monoenergetic gamma emitter uniformly distributed in an infinite cloud have been calulated by using the monoenergetic point-isotorpic source kernel technique. The most serious limitation on use of the kernel technique is subjected to the fact that it estimates the dose only at the surface of body. As a result, an alternative method is presented in which estimates of dose rate for immersion in a radioactive cloud are resulted from the scattered photon spectra incident on the surface of body. The results are in excellent agreement with other's. Work is currently in progress to apply these results to immersion dose problems associated with absorbed dose distribution in the MIRD phatom.

• Journal of radiological science and technology
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• v.43 no.2
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• pp.105-114
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• 2020

This study aimed to assess of beam-matching accuracy for an 8 MV beam between the same model linear accelerators(Linac) commissioned over two years. Two models were got the customer acceptance procedure(CAP) criteria. For commissioning data for beam-matched linacs, the percentage depth doses(PDDs), beam profiles, output factors, multi-leaf collimator(MLC) leaf transmission factors, and the dosimetric leaf gap(DLG) were compared. In addition, the accuracy of beam matching was verified at phantom and patient levels. At phantom level, the point doses specified in TG-53 and TG-119 were compared to evaluate the accuracy of beam modelling. At patient level, the dose volume histogram(DVH) parameters and the delivery accuracy are evaluated on volumetric modulated arc therapy(VMAT) plan for 40 patients that included 20 lung and 20 brain cases. Ionization depth curve and dose profiles obtained in CAP showed a good level for beam matching between both Linacs. The variations in commissioning beam data, such as PDDs, beam profiles, output factors, TF, and DLG were all less than 1%. For the treatment plans of brain tumor and lung cancer, the average and maximum differences in evaluated DVH parameters for the planning target volume(PTV) and the organs at risk(OARs) were within 0.30% and 1.30%. Furthermore, all gamma passing rates for both beam-matched Linacs were higher than 98% for the 2%/2 mm criteria and 99% for the 2%/3 mm criteria. The overall variations in the beam data, as well as tests at phantom and patient levels remains all within the tolerance (1% difference) of clinical acceptability between beam-matched Linacs. Thus, we found an excellent dosimetric agreement to 8 MV beam characteristics for the same model Linacs.

• Progress in Medical Physics
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• v.29 no.3
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• pp.92-100
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• 2018

The manufacturer of a linear accelerator (LINAC) has reported that the target melting phenomenon could be caused by a non-recommended output setting and the excessive use of monitor unit (MU) with intensity-modulated radiation therapy (IMRT). Due to these reasons, we observed an unexpected beam interruption during the treatment of a patient in our institution. The target status was inspected and a replacement of the target was determined. After the target replacement, the beam profile was adjusted to the machine commissioning beam data, and the absolute doses-to-water for 6 MV and 10 MV photon beams were calibrated according to American Association of Physicists in Medicine (AAPM) Task Group (TG)-51 protocol. To verify the beam data after target replacement, the beam flatness, symmetry, output factor, and percent depth dose (PDD) were measured and compared with the commissioning data. The difference between the referenced and measured data for flatness and symmetry exhibited a coincidence within 0.3% for both 6 MV and 10 MV, and the difference of the PDD at 10 cm depth ($PDD_{10}$) was also within 0.3% for both photon energies. Also, patient-specific quality assurances (QAs) were performed with gamma analysis using a 2-D diode and ion chamber array detector for eight patients. The average gamma passing rates for all patients for the relative dose distribution was $99.1%{\pm}1.0%$, and those for absolute dose distribution was $97.2%{\pm}2.7%$, which means the gamma analysis results were all clinically acceptable. In this study, we recommend that the beam characteristics, such as beam profile, depth dose, and output factors, should be examined. Further, patient-specific QAs should be performed to verify the changes in the overall beam delivery system when a target replacement is inevitable; although it is more important to check the beam output in a daily routine.

• Journal of Radiation Protection and Research
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• v.22 no.2
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• pp.85-95
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• 1997

TLD and film badges have been traditionally used as formal dosimeters in personal monitoring and are still most widely used. Recently, electronic personal dosimeters based upon Si diode or miniature G-M tube were developed and are getting attractions due to their merits of active nature ; indication of dose rates and the commutative dose, and facilitation of record keeping and radiological control. Response characteristics of the electronic dosimeters including reproducibility, accuracy, linearity, energy and angular dependencies, detection threshold, and response time were examined for three commercial types ; EPD2, STEPHEN6000, and PD-3i. The results were compared with the relevant requirements of IEC standards and Ontario Hydro standards to conclude that their general performances were good. Some specific deficiencies, e.g. incapability of shallow dose measurement of STEPHEN6000, and PD-3i, however, should be corrected to be used as a formal dosimeter.

• Progress in Medical Physics
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• v.22 no.4
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• pp.216-223
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• 2011

Recently PTW developed a MicroLion liquid ionization chamber which is water_equivalent and has a small sensitive volume of $0.002cm^3$. The aim of this work is to investigate such dosimetric characteristics as dose linearity, dose rate dependency, spatial resolution, and output factors of the chamber for the external radiotherapy photon beam. The results were compared to those of Semiflex chamber, Pinpoint chamber and Diode chamber with the sensitive volumes of $0.125cm^3$, $0.03cm^3$ and $0.0025cm^3$, respectively and evaluated to be suitable for small fields. This study was performed in the 6MV photon energy from a Varian 2300 C/D linac accelerator and the MP3 water phantom (PTW, Freiburg) was used. Penumbras in the varios field sizes ranged from $0.5{\times}0.5cm^2$ to $10{\times}10cm^2$ were used to evaluate the spatial resolution. Output factors were measured in the field sizes of $0.5{\times}0.5$ to $40{\times}40cm^2$. Readings of the chamber was linearly proportional to dose. Dose rate dependency was measured from 100 MU/min to 600 MU/min, showed a maximum difference of 5.0%, and outputs decreased with dose rates. The spatial resolutions determined with comparing profiles for the field sizes of $0.5{\times}0.5cm^2$ to $10{\times}10cm^2$ agreed between every detector except the Semiflex chamber to within 2%. Outputs of detectors were compared to that of Semiflex chamber and showed good agreements within 2% for every chamber. This study shows that MicroLion chamber characterized by a high signal-to-noise ratio and water equivalence could be suitable for the small field dosimetry.

• Nuclear Engineering and Technology
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• v.40 no.4
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• pp.319-326
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• 2008

To transport process wastes efficiently from the Advanced Spent Fuel Conditioning Pyro-process Facility (ACPF) at the Korea Atomic Energy Research Institute (KAERI), a new hot cell cask has been designed based on an existing hot cell padirac transport cask, with not only a neutron absorber for improved shielding capability, but also a docking facility for an easy docking system. In the new hot cell cask, two kinds of materials have been considered as shielding materials, polyethylene and resin. To verify the transport compatibility of the waste and spent fuel for the ACPF, neutron and photon shielding calculations were performed using the MCNPX code. The source term was evaluated by the ORIGEN-ARP code system based on spent PWR fuel. From the calculation, it was found that the maximum surface dose rates of the hot cell cask with the two candidates were estimated within the limit (2 mSv/hr).