• 대한방사선방어학회:학술대회논문집
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• 2011.11a
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• pp.198-199
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• 2011

• Proceedings of the Korean Society of Medical Physics Conference
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• 2005.04a
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• pp.96-99
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• 2005

본 연구에서는 식품의약품안전청의 도움을 받아 1998년부터 2003년까지 장기간에 걸친 교정정수의 분석을 통한 원통형이온함의 모델별 안정성을 확인하여 보다 효율적인 이온함의 선택으로 방사선치료기관의 선량측정체계의 정확도 향상에 기여하고자 한다. 방사선치료기관에서 사용하고 있는 Farmer형의 원통형이온함에 대한 에어커마 교정정수(NK)를 분석한 결과 Wellhofer FC65G (IC70)와 PTW 30001, 30013 (30006) 그리고 NE 2571 이온함 모델에 대한 교정정수는 모두 0.3%이내에서 잘 일치하였다. 또한 에어커마 교정정수를 이용하여 계산된 물 흡수선량 교정정수(Cal. ND,W)와 실제 측정에 의해 결정된 물 흡수선량 교정정수(Mea. ND,W)를 비교한 결과는 약 1.0% 정도 측정에 의한 교정정수가 높게 나타났으며 에어커마 교정정수를 분석한 결과와 마찬가지로 위 동일한 모델의 이온함에 대해서 측정의 표준편차가 0.14～0.17%로 나타나 장기적인 안정성이 입증되었다.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2004.11a
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• pp.149-152
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• 2004

물 흡수선량 표준에 토대를 두고 있는 프로토콜에서는 저에너지 전자선의 경우 평행평판형이온함의 사용과 기준 선질 $^{60}$CO 감마선의 물 흡수선량 교정정수를 받은 원통형이온함을 사용하여 고에너지 전자선에서 평행평판형이온함을 교차교정하도록 권고하고 있다. 따라서 본 연구에서는 국제원자력기구의 프로토콜(IAEA TRS-398)에서 권고하고 있는 절차에 따라 저에너지 전자선에 대한 원통형이온함의 선질보정정수를 계산하고, 원통형이온함과 평행평판형이온함의 교정방법에 따른 흡수선량을 상호 비교하였다. 그 결과 전자선에너지 10 MeV 이상에서는 두 이온함간의 선량이 잘 일치하였으나 전자선에너지 6, 9 MeV에서 최대 3.3%까지 선량 차이를 보여 저에너지 전자선에서는 반드시 평형판판형이온함의 사용하여 선량측정 할 것을 권고한다. 교정방법 차이에 의한 평행평판형이온함의 선량은 서로 잘 일치하는 것으로 나타나 표준기관에서 직접 교정받은 $^{60}$Co 감마선의 물 흡수선량교정정수를 사용하여 전자선 물 흡수선량을 결정해도 큰 영향은 없을 듯하다. 또한 평행평판형이온함을 교차 교정하기 위한 전자선 에너지에 따른 흡수선량을 상호 비교한 결과 20MeV이외 12, 16 MeV의 전자선 에너지에서도 잘 일치하여 교차교정을 위한 전자선의 기준 선질에 대한 연구가 더 진행되어야 한다고 사료된다.

• Progress in Medical Physics
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• v.14 no.4
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• pp.249-258
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• 2003

A few years ago, a proposal was made to change the dosimetry from the air kerma-based reference dosimetry to the absorbed dose-based reference dosimetry for all radiotherapy beams of ionizing radiation to improve the accuracy of dosimetry. Here, we present a dosimetry study in which the two most widespread absorbed dose­based protocols (IAEA TRS­398 and AAPM TG­51) were compared with an air kerma­based protocol (IAEA TRS-277) by measuring the absorbed dose in the same reference depth. Measurements were performed in three clinical electron beam energies using a PTW 30002 cylindrical chamber, and Markus and Roos plane­parallel chambers. $^{60}$ Co calibration factors were obtained from the KFDA. The absorbed dose differences between the air kerma­based and absorbed dose­based protocols were within 2.0% for all chambers in all beams. The results thus show that the obtained absolute dose values will be not significantly altered by changing from the air kerma­based dosimetry to the absorbed dose­based dosimetry. It was also shown that absorbed dose values between the absorbed dose­based protocols agreed by deviations of less than 0.5% for a cylindrical chamber and less than 0.7% for plane­parallel chambers using cross­calibration factors. Although the use of a cylindrical chamber and plane­parallel chambers resulted in a difference of less than 2% for all situations investigated here, to reduce errors, the plane­parallel chambers are recommended for electron energies in which the use of cylindrical chamber is not permitted in each protocol.

• Progress in Medical Physics
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• v.21 no.1
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• pp.120-125
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• 2010

For the measurements of an absorbed dose using the standard dosimetry based on an absorbed dose to water the variety of factors, whether big, small, or tiny, may influence the accuracy of dosimetry. The beam quality correction factor ${\kappa}_{Q,Q_0}$ of an ionization chamber might also be one of them. The cylindrical type of ionization chamber, the PTW30013 chamber, was chosen for this work and 9 chambers of the same type were collected from several institutes where the chamber types are used for the reference dosimetry. They were calibrated from the domestic Secondary Standard Dosimetry Laboratory with the same electrometer and cable. These calibrated chambers were used to measure absorbed doses to water in the reference condition for the photon beam of 6 MV and 10 MV and the electron beam of 12 MeV from Siemens ONCOR. The biggest difference among chambers amounts to 2.4% for the 6 MV photon beam, 0.8% for the 10 MV photon beam, and 2.4% for the 12 MeV electron beam. The big deviation in the photon of 6 MV demonstrates that if there had been no problems with the process of measurements application of the same ${\kappa}_{Q,Q_0}$ to the chambers used in this study might have influenced the deviation in the photon 6 MV and that how important an external audit is.

• Progress in Medical Physics
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• v.16 no.2
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• pp.77-81
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• 2005

To determine the appropriate method out of various available methods to measure build-up doses, the measurements and comparisons of depth doses of build-up region including the surface dose were executed using the Attix parallel-plate ionization chamber, the Markus chamber, a cylindrical ionization chamber, and a diode detector. Based on the measurements using the Attix chamber, discrepancies of the Markus chamber were within $2\%$ for the open field and increased up to $3.9\%$ in the case of photon beam containing the contaminant electrons. The measurements of an cylindrical ionization chamber and a diode detector accord with those of the Attix chamber within $1.5\%\;and\;1.0\%$ and after those detectors were completely immersed in the water phantom. The results suggest that the parallel-plate chamber is the best choice to measure depth doses in the build-up region containing the surface, however, using cylindrical ionization chamber or diode detector would be a reasonable choice if no special care is necessary for the exact surface dose.

• Journal of Radiation Protection and Research
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• v.24 no.4
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• pp.195-203
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• 1999

It is difficult to determine dosimetric characteristics for small field photon beams since such small fields do not achieve complete lateral electronic equilibrium and have steep dose gradients. Dosimetric characteristics of small field 4, 6, and 10 MeV photon beams have been measured in water with a diamond detector and compared to measurements using small volume cylindrical and plane parallel ionization chambers. Percent depth dose (PDD) and beam profiles for 6 and 10 MeV photon beams were measured with diamond detector and cylindrical ion chamber for small fields ranging from $1{\times}1\;to\;4{\times}4cm^2$. Total scatter factors($S_{c,p}$) for 4, 6, and 10 MeV photon beams were measured with diamond detector, cylindrical and plane parallel ion chambers for small fields ranging from $1{\times}1\;to\;4{\times}4cm^2$. The $S_{c,p}$ factors obtained with three detectors for 4, 6, and 10 MeV photon beams agreed well ($\pm1.2%$) for field sizes greater than $2{\times}2,\;2.5{\times}2.5,\;and\;3{\times}3\;cm^2$, respectively. For smaller field sizes, the cylindrical and plane parallel ionization chambers measure a smaller $S_{c,p}$ factor, as a result of the steep dose gradients across their sensitive volumes. The PDD values obtained with diamond detector and cylindrical ionization chamber for 6 and 10MeV photon beams agreed well ($\pm1.5%$) for field sizes greater than $4{\times}4\;cm^2$. For smaller field sizes, diamond detector produced a depth-dose curve which had a significantly shallower falloff than that obtained from the measurements of relative depth-dose with a cylindrical ionization chamber. For the measurements of beam profiles, a distortion in terms of broadened penumbra was observed with a cylindrical ionization chamber since diamond detector exhibited higher spatial resolution. The diamond detector with small sensitive volume, near water equivalent, and high spatial resolution is suitable detector compared to ionization chambers for the measurements of small field photon beams.

• Progress in Medical Physics
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• v.20 no.4
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• pp.317-323
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• 2009

The standard dosimetry systems based on an absorbed dose to water recommend to use a planeparallel chamber for the calibration of such a low-megavoltage electron beam as a nominal energy of 6 MeV. For this energy ranges of an electron beam a cylindrical chamber should not be used for the routinely regular beam calibration, but the feasibility of the temporary use of a cylindrical chamber was studied to give temporary solutions for special situations users meet. The PTW30013 chambers and the electron beam quality of $R_{50}=2.25\;g/cm^2$ were selected for this study. 10 PTW30013 chambers, a cylindrical type of chamber, were calibrated in KFDA, the secondary standards dosimetry laboratories, and given the absorbed dose-to-water calibration factors, respectively. A "temporary" $k_{Q,Q_0}$ for each chamber were calculated using the absorbed dose determined by a cross-calibrated planeparallel chamber, with the result of an average 0.9352 for 10 chambers. This value for PTW30013 chamber was used to determine an absorbed dose to water at the reference depth. The absorbed doses determined by PTW30013 chambers were in an agreement within 2% with that by ROOS chamber. In a certain situation where a cylindrical chamber be used instead of a planeparellel chamber, the value of 0.9352 might be useful to determine an absorbed dose to water in the same beam quality of electron beam as this study.

• Progress in Medical Physics
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• v.20 no.1
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• pp.7-13
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• 2009

This work is for the preliminary study for the calibration of an $^{192}Ir$ brachytherapy source based on an absorbed dose to water standards. In order to calibrate brachytherapy sources based on absorbed dose to water standards using a clyndirical ionization chamber, the beam quality correction factor $k_{Q,Q_0}$ is needed. In this study $k_{Q,Q_0}s$ were determined by both Monte carlo simulation and semiexperimental methods because of the realistic difficulties to use primary standards to measure an absolute dose at a specified distance. The 5 different serial numbers of the PTW30013 chamber type were selected for this study. While chamber to chamber variations ran up to maximum 4.0% with the generic $k^{gen}_{Q,Q_0}$, the chamber to chamber variations were within a maximum deviation of 0.5% with the individual $k^{ind}_{Q,Q_0}$. The results show why and how important ionization chambers must be calibrated individually for the calibration of $^{192}Ir$ brachytherapy sources based on absorbed dose to water standards. We hope that in the near future users will be able to calibrate the brachytherapy sources in terms of an absorbed dose to water, the quantity of interest in the treatment, instead of an air kerma strength just as the calibration in the high energy photon and electron beam.

• Progress in Medical Physics
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• v.13 no.2
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• pp.55-61
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• 2002

In this work, EPM (effective point of measurement) of parallel plate ionization chamber with three different spacing were investigated. If the plate separation is less than 2 mm one generally assumes that the effective point of measurement is just behind the front window of the parallel plate ionization chamber. For chamber with relatively large separation, such as the ones used for very accurate exposure measurements, this assumption breaks down and the EPM depends on plate separation and thickness of the front window. For parallel plate chambers, conventional theoretical analyses suggest that the EPM is the inner front wall and that it shifts towards the geometric centre of the chamber as the plate separation increases. The PP-IC (parallel plate ionization chamber) is fabricated using acrylic plate for the chamber medium and printed circuit board for electrical configuration. The various sizes of the sensitive volumes designed so far are 0.9, 1.9, and 3.1 cc. The gap between two electrodes ranges from 3, 6, and 10mm. Also the charge-to-voltage converter is designed to collect the electrons produced in the ionization chamber cavity. As the result of our experiment, the EPM shift was within 0.6 mm in photon beams and 0.4 mm to 2.5 mm in electron beams for the plate separation of 6 mm and 10 mm. EPM shifts towards the geometric center of the chamber as the plate separation increases.