• Progress in Medical Physics
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• v.9 no.1
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• pp.55-64
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• 1998

In recent, the demand of development of the high dose rate brachytherapy source increased for substitute for Co-60 source by iridium source, since the supplying Co-60 source is very depressed and the high dose rate brachytherapy sources are entirely imported from the abroad. This study investigated the exposure rates and isotropic dose distributions for the Ir-192 source produced from $\^$191/Ir(n,r)$\^$192/Ir by nuclear reactor in Korea Atomic Energy Research Institute. The activity of source was obtained an 1.012 Ci (the initial activity without encapsulation was 2,87Ci) by measurement with encapsuled stainless steel. The exposure rate of provided Ir-192 source was determined on 6.36 ${\pm}$ 0.147 Rm$^2$/h-GBq (2.350 ${\pm}$ 0.054 Rcm$^2$/mCi-hr) within ${\pm}$ 2.2% discrepancy with IC-10 ion chamber (0.14 cc) which was mounted on the acrylic jig to 5, 10 and 20 cm from the center of source. The calculated doses with 22 most significant spectrum lines were corrected with intrinsic efficiency of the germanium detector were compared to measured exposure dose rates within ${\pm}$3.8 % discrepancy. The authors confirmed the high dose rate Ir-192 source could be replaced the long decayed Co-60 source via investigation of the isotropic dose distributions in lateral, source axis and diagonal direction of source center are very closed to within 3% uncertainties. Especially, this exposure rate constant and isotropic dose distribution will be fundamental to build the high dose rate source and develop the computed therapy planning system.

• Progress in Medical Physics
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• v.9 no.4
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• pp.259-266
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• 1998

To achieve the 2D dose distribution around the designed high dose rate Ir-192 source substitution for Co-60 brachytherapy source, we determined the exposure rate constant and tissue attenuation factors as a large depth as a 20 cm from source center. The exposure rate constant is used for apparent activity in designed source with self-absorption and encapsulation steel wall. The tissue dose delivered from the 4401 segments of 2.5 mm in a diameter and 2.5 mm height of disk-type source layer. In the experiments, the tissue attenuation factors include the tissue attenuation and multiple scattering in a medium surrounding the source. The fitted the polynomial regression with 4th order for the tissue attenuation factors are very closed to the experimental measurement data within ${\pm}$1% discrepancy. The Meisberger's constant showed the large uncertainty in large distance from source. The exposure rate constant 4.69 Rcm$^2$/mCi-hr was currently used for determination of apparent activity of source and air kerma strength was obtained 0.973 for tissue absorbed dose from the energy spectrum of Ir-192 source. In our experiments with designed high dose rate brachytherapy source, the apparent activity of Ir-192 source was delivered from the 54.6 % of actual physical source activity through the self-absorption and encapsulation wall attenuations. This paper provides the 2-dimensional dose tabulation from unit apparent activity in a water medium for dose planning includes the multiple scattering, source anisotropy effect and geometric factors.

• Korean Journal of Environmental Biology
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• v.20 no.4
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• pp.277-286
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• 2002

An increase in the overall biological effect under the combined action of ionizing radiation with another inactivating agent can be explained in two ways. One is the supposition that synergism may attribute to a reduced cellular capacity of damn-ge repair after the combined action. The other is the hypothesis that synergism may be related to an additional lethal or potentially lethal damage that arises from the interaction of sublesions induced by both agents. These sublesions ave considered to be in-effective when each agent is applied separately. Based on this hypothesis, a simple mathematical model was established. The model can predict the greatest value of the synergistic effect, and the dependence of synergy on the intensity of agents applied, as well. This paper deals with the model validation and the peculiarity of simultaneous action of various factors with radiation on biological systems such as bacteriophage, bacterial spores, yeast and mammalian cells. The common rules of the synergism aye as follows. (1) For any constant rate of exposure, the synergy can be observed only within a certain temperature range. The temperature range which synergistically increases the effects of radiation is shifted to the lower temperature fer thermosensitive objects. Inside this range, there is a specific temperature that maximizes the synergistic effect. (2) A decrease in the exposure rate results in a decrease of this specific temperature to achieve the greatest synergy and vice versa. For a constant temperature at which the irradiation occurs, synergy can be observed within a certain dose rate range. Inside this range an optimal intensity of the physical agent may be indicated, which maximizes the synergy. As the exposure temperature reduces, the optimal intensity decreases and vice versa. (3) The recovery rate after combined action is decelerated due to an increased number of irreversible damages. The probability of recovery is independent of the exposure temperature for yeast cells irradiated with ionizing or UV radiation. Chemical inhibitors of cell recovery act through the formation of irreversible damage but not via damaging the recovery process itself.

• Journal of radiological science and technology
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• v.19 no.2
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• pp.71-77
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• 1996

Studies were conducted to determine the clinical application of photodiode. We compared photodiode with ion-chamber as to change of tube potential, tube current, mAs and measured decreasing rate of penetration dose. When tube potential was changed from 60 kVp to 120 kVp, output of photodiode and ion-chamber were changed from 0.4 to 1.625, and 1.018 to 4.268, respectively. This was a good agreement to theory that $I=Kv^2it$(I is intensity, K is constant, v is tube potential, i is tube current, t is time). Characteristics for change of tube current and mAs were also a good agreement to theory. And comparison in decreasing rate of penetration dose was similar except above 6 cm in depth. Our results indicated that photodiode was a good instrument for relative measurement of radiation exposure, but we can not use the photodiode for absolute radiation dose.

• Journal of Radiation Protection and Research
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• v.12 no.1
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• pp.1-11
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• 1987

Central axis percentage depth-doses, P(%), were measured at the points from the 2.5cm depth of reference point to 20 cm depth with 2.5 cm interval. Distance from the X-ray target to the water phantom($30{\times}30{\times}30cm^3$) surface was 1 m, and at this point three different beam sizes of $5cm{\phi},\;10cm{\phi},\;and\;15cm{\phi}$ were used. While the X-ray tube voltage varied from 150 to 250 kV, the tube current remained constant at 5 mA. Absorbed dose rate in water, $\dot{D}_w$, was determined using the air kerma calibration factor, $N_k$, which was derived from the exposure calibration factor, $N_x$, of the NE 2571 ion chamber. The reference exposure rate, $\dot{X}_c$, was measured using the Exradin A-2 ion chamber calibrated at ETL, Japan. The half value layers of the X-rays determined to meet ETL calibration qualities. The absorbed dose rates determined at the calibration point were compared to the values obtained from Burlin's general cavity theory, and the percentage depth-dose values determined from $N_k$ showed a good agreement with the values of the published depth dose data(BJR Suppl. 17).

• Journal of the Korean Society of Radiology
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• v.14 no.3
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• pp.279-287
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• 2020

Recently, interest in radiation protection is increasing because of the occurrence of accidents related to exposure dose. So, the nuclear safety act provides to install the shields to avoid exceeding the dose limit. In particular, when the worker conducts the non-destructive testing (NDT) without the fixed shielding structure, we should monitor the access to the workplace based on a constant dose rate. However, when we apply for permits for NDT work in these work environments, the consideration factors to the estimation of the distance and exposure dose are not legally specified. Therefore, we developed the excel model that automatically calculates the distance, exposure dose, and cost if we input the factors. We applied the assumption data to this model. As a result of the application, the distance change rate was low when the thickness of the lead blanket and collimator is above 25 mm, 21.5 mm, respectively. However, we didn't consider the scattering and build-up factor. And, we assumed the shape of the lead blanket and collimator. Therefore, if we make up for these limitations and use the actual data, we expect that we can build a database on the distance and exposure dose.

• The Korean Journal of Nuclear Medicine Technology
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• v.20 no.1
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• pp.28-31
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• 2016

Purpose $^{223}Ra-Dichloride$ is used for the medicine of castration-resistant prostate cancer (CRPC) and which emits ${\alpha}-ray$ of 28 Mev that is used for therapy. However $^{223}Ra-Dichloride$ emits ${\beta}-ray$ of 3.6% and ${\gamma}-ray$ of 1.1%(80,156,270 keV) aside from ${\alpha}-ray$ in decay. Therefore we would like to evaluate external radiation expose dose rate of ${\gamma}-ray$ of $^{223}Ra-Dichloride$. Materials and Methods We calculated external radiation expose dose rate using ${\gamma}-constant$ of $^{223}Ra-Dichloride$, $^{99m}Tc$ based on Health physics(2012). $^{223}Ra-Dichloride$ of 3.5 MBq and $^{99m}Tc-MDP$ of 740 MBq were applied. external radiation expose dose rate 15 times from 1m by survey meter. Results ${\gamma}-contant$ of $^{223}Ra$, $^{99m}Tc-MDP$ from 1m distance based on Health physics(2012) is 0.0469, 0.0215. calculated value of external radiation expose dose rate was $16{\mu}Sy$, $34{\mu}Sy$ which activity is $^{223}Ra-Dichloride$ of 3.5 MBq and $^{99m}Tc-MDP$ of 740 MBq from 1 m and measured mean value of 1 m was $0.7{\mu}Sy/h$, $18{\mu}Sy/h$. Conclusion ${\gamma}-constant$ of $^{223}Ra$ is higher than $^{99m}Tc$ based on Health physics(2012). however calculated maximum external radiation expose dose rate of $^{223}Ra-Dichloride$ is lower than $^{99m}Tc$ due to actually used quantity of activity of $^{223}Ra-Dichloride$ is small. measured value of $^{223}Ra-Dichloride$ is also lower than $^{99m}Tc-MDP$. Therefore external radiation expose dose rate of ${\gamma}-ray$ of $^{223}Ra-Dichloride$ is very low.

• Korean Journal of Environmental Biology
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• v.20 no.2
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• pp.165-172
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• 2002

The combined action of two factors on organisms can be either antagonistic, non-effective, additive or synergistic. Although synergism is of biological importance, the common features of synergistic interaction between harmful environmental factors are largely unknown. The purpose of this study is to establish general rules describing the response of various organisms to the combined action of heat with another inactivating agent. Synergistic interaction due to the simultaneous treatment of hyperthermia with ionizing or non-ionizing radiation has been analyzed using the experimental data mainly obtained with yeast cells. In addition, the results reported by others for viruses, bacterial spores, cultured mammalian cells, plants and animals were also analyzed to check the regularities revealed. The common rules of the synergistic interaction obtained in this study can be summarized as follows. For any constant rate of exposure, the synergy can be observed only within a certain temperature range. An increase in exposure rate resulted in an increase of this specific temperature and vice versa. For a constant temperature at which the irradiation occurs, synergy can be observed within a certain dose rate range. As the exposure temperature is reduced, the optimal intensity decreases and vice versa. A new conception taken into consideration those regularities can make a clue for environmental disaster preventive analysis of the synergy of radiation with the other factor.

• Journal of the Korean Society of Radiology
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• v.12 no.7
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• pp.845-852
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• 2018

This study aimed to investigate the difference of X-ray exposure by comparing and analyzing absorbed dose according to changes in the number of frames in coronary angiography, also depending whether the zoom mode is FOV enlargement or Zoom Live. Moreover, for appropriate frame selection measures for examination, including the effect of frame change on the image quality, were sought by measuring the noise strength expressed by the standard deviation (SD), the signal to noise ratio (SNR) and contrast to noise ratio (CNR). The study was conducted with an anthropomorphic phantom on an angio-system. The linear relationship between the frame rate and the radiation dose was evident. On the contrary, the indices of image quality (SD, SNR, and CNR) were almost constant irrespective of the number of frames. The difference depending on the zoom mode was not statistically significant for DAP, air kerma, and SD (p > 0.05). However, SNR and CNR were statistically different between FOV enlargement and Zoom Live. In conclusion, since the image quality was not degraded significantly with the decreasing frame rate from 30, 15, to 7.5 f/s and the radiation dose evidently decreases in almost exactly linear proportion to the decreasing frame rate, the number of frames per second needs to be maintained as low as reasonably achievable. As for the dependence on the zooming mode, the Live Zoom mode showed statistically significant improvement in the image quality indices of SNR and CNR and it justifies active use of the Live Zoom mode which enables real-time image enlargment without additional radiation dose.

• Journal of Radiation Protection and Research
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• v.19 no.1
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• pp.51-68
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• 1994

It is good method to use frequency of chromosome aberration in Lymphocytes for a biological dosimetry in cases of accidental exposure to radiation. But in cases of past exposure, biological dosimetry is limited because the frequency of aberration decreases by time after exposure. To provide a basic data for estimation of past radiation exposure, the changing pattern of frequency of unstable chromosome aberration by time interval after exposure was studied. Observation was made on peripheral lymphocytes of 41 blood samples from 20 patients treated for uterine cervical carcinoma and endometrial carcinoma. The patients received 50.4Gy radiation to whole pelvis. Elapsed times after the completion of radiation therapy were 1 day, 3, 6, 9, 12, 24, 52, 104, 156, 208, 260 and 520 weeks. All the blood sample were microcultured. The Ydr, Qdr and Qdra were calculated from frequency of unstable aberration. Ydr did not decrease for 3 weeks after radiation therapy, and thereafter, decreased very rapidly and reached 0.05 at two years after radiation therapy and decreased very slowly until 5 years after radiation therapy. Relationship between unstable chromosome aberration and time interval after radiation therapy was described as $Ydr=0.259{\times}exp(-0.0429T)+0.0560{\times}exp(-0.00106T)$ (time in weeks) Qdr remained constant at 1.51 until 24 weeks after radiation therapy and then decreased to 1.17 at 52 weeks. Therafter, it did not change. Qdra remained constant at 1.10 for 12 weeks after radiation therapy and decreased to 0.81 at 52 weeks. Thereafter, it remained constant. Two superimposed exponential Ydr disappearance rate suggests that it is possible to calculate the past exposure dose. When the elapsed time after exposure is short, Qdr and Qdra are useful papameters for biological dosimetry for past radiation exposure.