• Nuclear Engineering and Technology
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• 제55권8호
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• pp.2935-2940
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• 2023

A polystyrene phantom was developed following the guidance of the International Atomic Energy Association (IAEA) for gamma knife (GK) quality assurance. Its performance was assessed by measuring the absorbed dose rate to water and dose distributions. The phantom was made of polystyrene, which has an electron density (1.0156) similar to that of water. The phantom included one outer phantom and four inner phantoms. Two inner phantoms held PTW T31010 and Exradin A16 ion chambers. One inner phantom held a film in the XY plane of the Leksell coordinate system, and another inner phantom held a film in the YZ or ZX planes. The absorbed dose rate to water and beam profiles of the machine-specific reference (msr) field, namely, the 16 mm collimator field of a GK Perfexion^TM or Icon^TM, were measured at seven GK sites. The measured results were compared to those of an IAEA-recommended solid water (SW) phantom. The radius of the polystyrene phantom was determined to be 7.88 cm by converting the electron density of the plastic, considering a water depth of 8 g/cm². The absorbed dose rates to water measured in both phantoms differed from the treatment planning program by less than 1.1%. Before msr correction, the PTW T31010 dose rates (PTW Freiberg GmbH, New York, NY, USA) in the polystyrene phantom were 0.70 (0.29)% higher on average than those in the SW phantom. The Exradin A16 (Standard Imaging, Middleton, WI, USA) dose rates were 0.76 (0.32)% higher in the polystyrene phantom. After msr correction factors were applied, there were no statistically significant differences in the A16 dose rates measured in the two phantoms; however, the T31010 dose rates were 0.72 (0.29)% higher in the polystyrene phantom. When the full widths at half maximum and penumbras of the msr field were compared, no significant differences between the two phantoms were observed, except for the penumbra in the Y-axis. However, the difference in the penumbra was smaller than variations among different sites. A polystyrene phantom developed for gamma knife dosimetry showed dosimetric performance comparable to that of a commercial SW phantom. In addition to its cost effectiveness, the polystyrene phantom removes air space around the detector. Additional simulations of the msr correction factors of the polystyrene phantom should be performed.

• 대한방사선치료학회지
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• 제10권1호
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• pp.11-22
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• 1998

The absolute absorbed dose can be determined according to the measurement conditions ; measurement material, detector, energy and calibration protocols. The purpose of this study is to compare the absolute absorbed dose due to the differences of measurement condition and calibration protocols for photon beams. Dosimetric measurements were performed with a farmer type PTW and NEL ionization chambers in water, solid water, and polystyrene phantoms using 6MV photon beams from Siemens linear accelerator. Measurements were made along the central axis of $10{\times}10cm$ field size for constant target to surface distance of 100cm for water, solid water and polystyrene phantom. Theoretical absorbed dose intercomparisons between TG21 and IAEA protocol were performed for various measurement combinations on phantom, ion chamber, and electrometer. There were no significant differences of absorbed dose value between TG2l and IAEA protocol. The differences between two protocols are within $1\%\;while\;the\;average\;value\;of\;IAEA\;protocol\;was\;0.5\%$ smaller than TG2l protocol. For the purpose of comparison, all the relative absorbed dose were nomalized to NEL ion chamber with Keithley electrometer and water phantom, The average differences are within $1\%,\;but\;individual\;discrepancies\;are\;in\;the\;range\;of\;-2.5\%\;to\;1.2\%$ depending upon the choice of measurement combination. The largest discrepancy of $-25\%$ was observed when NEL ion chamber with Keithley electrometer is used in solid water phantom. The main cause for this discrepancy is due to the use of same parameters of stopping power, absorption coefficient, etc. as used in water phantom. It should be mentioned that the solid water phantom is not recommended for absolute dose calibration as the alternative of water, since absorbed dose show some dependency on phantom material other than water. In conclusion, the trend of variation was not much dependent on calibration protocol. However, It shows that absorbed dose could be affected by phantom material other than water.

• Nuclear Engineering and Technology
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• 제43권4호
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• pp.399-404
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• 2011

A LEGO-type multi-purpose dosimetry phantom was developed for intensity-modulated radiation therapy (IMRT), which requires various types of challenging dosimetry. Polystyrene, polyethylene, polytetrafluoroethylene (PTFE), and polyurethane foam (PU-F) were selected to represent muscle, fat, bone, and lung tissue, respectively, after considering the relevant mass densities, elemental compositions, effective atomic numbers, and photon interaction coefficients. The phantom, which is composed of numerous small pieces that are similar to LEGO blocks, provides dose and dose distribution measurements in homogeneous and heterogeneous media. The phantom includes dosimeter holders for several types of dosimeters that are frequently used in IMRT dosimetry. An ion chamber and a diode detector were used to test dosimetry in heterogeneous media under radiation fields of various sizes. The data that were measured using these dosimeters were in disagreement when the field sizes were smaller than $1.5{\times}1.5\;cm^2$ for polystyrene and PTFE, or smaller than $3{\times}3\;cm^2$ for an air cavity. The discrepancy was as large as 41% for the air cavity when the field size was $0.7{\times}0.7\;cm^2$, highlighting one of the challenges of IMRT small field dosimetry. The LEGO-type phantom is also very useful for two-dimensional dosimetry analysis, which elucidates the electronic dis-equilibrium phenomena on or near the heterogeneity boundaries.

• Radiation Oncology Journal
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• 제12권2호
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• pp.225-232
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• 1994

연구목적 : 전남대학교병원 치료방사선과에서 가동중인 10MV X-ray를 이용하여 전신 방사선 조사에 필요한 기본적인 선량측정자료를 얻고자 하였다. 대상 및 방법 : 환자 전신이 포함될 수 있는 대형조사면을 얻기 위하여 collimator를 완전히 개방하여 조사방향이 수평이 되게 gantry각을 맞추었다. 방사선 선원에서 환자 중심축까지의 거리가 360cm일 때 최대 기하학적 조사면은 $144cm{\times}144cm$이었다. Polystyrene팬텀과 평행평판형 전리함을 이용하여 깊이선량율과 principal 및 diagonal axis에서 측방선량분포를 측정하였다. 또한 1cm두께의 아크릴판을 팬텀의 전면에서 20cm 떨어진 위치에 놓고 표면 선량의 증가와 최대선량점($d_{max}$)의 변화를 측정하였다. SAD 360cm에서 팬텀의 중심에 측정기 위치를 고정시키고 팬텀의 두께를 12cm에서 30cm까지 변화시키면서 MU당 선량율을 측정하였다. 결과 : SSD 345cm, 조사면 크기 $144cm{\times}144cm$의 조건에서 깊이선량율은 10cm 깊이에서 $78.4{\%}$였고, dmax정은 1.8cm이었다. 1cm두께의 아크릴판을 spoiler로 팬텀에서 20cm 띄우고 사용했을 때 dmax점은 1.8cm에서 0.8cm으로 이동하였고, 표면선량은 $61\%$에서 $94\%$로 증가하였다. 평행 2문 조사시 30cm두께의 팬텀에서 선축상 선량분포의 차이는 $7\%$이내였다. $100\%$ 선량점의 선축이탈거리는 principal axis에서 67cm. diagonal axis에서 80cm이었다. 팬텀의 중심에서 측정된 출력계수로 MU당 선량은, (Dose/MU)=$-0.00178{\times}(T/2)+0.08676$ (T:팬텀 두께(Cm))로 표현되는 직선의 관계식을 나타내었다. 결론 : 1)좌우 대향 2문조사 방법으로 30cm두께의 팬텀에 10MV X-ray를 조사하였을 때 선량분포의 차이는 $7\%$이내로 만족스러운 결과를 보였다. 2) 고에너지 광자선으로 전신방사선 조사시 표면선량 증가를 위하여 beam spotter의 사용이 필요할 것으로 사료된다 3) 측방선량분포곡선에서 principal 및 diagonal axis에 따른 선량분포의 차이가 있어 환자 치료시 고려되어야 할 것으로 생각된다 4) 전신방사선조사시 선량분포는 여러 가지 요인에의하여 달라질 수 있기 때문에 직접적인 방법에 의해 측정된 MU당 선량은 깊이와 직선의 관계식을 보여 실제 치료에 적용될 수 있을 것으로 생각된다. 본 연구에서 얻어진 전신 방사선조사에 관한 기본적 선량측정자료는 AAPM보고서 No. 17에서 권장된 범주에 들었으며 향후 임상에 이용될 수 있을 것으로 생각된다.

• 대한방사선기술학회지:방사선기술과학
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• 제31권1호
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• pp.83-87
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• 2008

본 연구의 목적은 고체물등가팬텀을 사용하여 절대흡수선량을 측정할 때 물등가깊이에 비례되는 측정값을 보정하기 위한 보정인자를 구하는데 있다. 10MV X-선 빔에 대하여 백색폴리스티렌팬텀과 물팬텀에서 측정의 조건들은 선원 대 전리조 중심까지의 거리를 SAD 100 cm로 고정하였고, 조사면 크기(field size)는 각각 $10{\times}10\;cm^2$, $20{\times}20\;cm^2$를 사용하였으며, 깊이는 각각 2.3 cm, 5 cm, 10 cm, 15 cm를 사용한 것이다. 두 개의 팬텀에 대하여 분당 400 MU의 출력을 갖는 선형가속기로부터 100 MU의 전달로 각각의 조사면 크기와 깊이들에서 3번 측정으로 취득된 전리의 평균값을 측정값으로 얻었다. 이 실험으로부터 보정인자와 TPR에서 퍼센트 편차는 각각 0.97%, 0.53% 이하를 얻었다. 따라서, 고체물등가팬텀을 사용한 절대흡수선량 측정 시에는 보정인자와 TPR에서 퍼센트 편차를 사용하여 보정을 행하면 높은 정확도를 얻을 수 있다.

• Journal of Radiation Protection and Research
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• 제42권1호
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• pp.9-15
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• 2017

Background: The purpose of this study is to assign an appropriate density to virtual phantom for 2D diode array detector with different dose calculation algorithms to guarantee the accuracy of patient-specific QA. Materials and Methods: Ten VMAT plans with 6 MV photon beam and ten VMAT plans with 15 MV photon beam were selected retrospectively. The computed tomography (CT) images of MapCHECK2 with MapPHAN were acquired to design the virtual phantom images. For all plans, dose distributions were calculated for the virtual phantoms with four different materials by AAA and AXB algorithms. The four materials were polystyrene, 455 HU, Jursinic phantom, and PVC. Passing rates for several gamma criteria were calculated by comparing the measured dose distribution with calculated dose distributions of four materials. Results and Discussion: For validation of AXB modeling in clinic, the mean percentages of agreement in the cases of dose difference criteria of 1.0% and 2.0% for 6 MV were $97.2%{\pm}2.3%$, and $99.4%{\pm}1.1%$, respectively while those for 15 MV were $98.5%{\pm}0.85%$ and $99.8%{\pm}0.2%$, respectively. In the case of 2%/2 mm, all mean passing rates were more than 96.0% and 97.2% for 6 MV and 15 MV, respectively, regardless of the virtual phantoms of different materials and dose calculation algorithms. The passing rates in all criteria slightly increased for AXB as well as AAA when using 455 HU rather than polystyrene. Conclusion: The virtual phantom which had a 455 HU values showed high passing rates for all gamma criteria. To guarantee the accuracy of patent-specific VMAT QA, each institution should fine-tune the mass density or HU values of this device.

• 한국의학물리학회지:의학물리
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• 제8권2호
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• pp.87-102
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• 1997

목적 : 방사선량 측정시 에너지, 매질, 측정기 등의 측정 조건과 측정 프로토콜에 따라 절대 흡수선량값이 결정된다. 본 연구에서는 이러한 측정 조건의 변화와 측정 프로토콜의 차이에 따른 절대 선량 값을 구하여 비교 분석 하고자 한다. 방법 : 시멘스 선형가속기에서 발생하는 6MV 광자선을 이용하여 3개의 다른 매질(물, 고체 물팬텀, 폴리스틸렌팬텀)내에서 2개의 전리함 (PTW ion chamber, NEL ion chamber)과 2개의 전기계(Victoreen electrometer, Keithley electrometer)를 사용하여 흡수선량을 측정하였다. 매질, 전리함, 전기계등의 측정 조건을 달리하여 서로 다른 조합에 대한 측정값을 TG21, IAEA 프로토콜에 의해 각각 분석하였다. 결과 및 결론 : 2개의 전기계와 2개의 전리함 조합에 따른 TG2l 및 IAEA 의 Ngas,, ND값의 비는 평균적으로 1％ 이내에서 일치하였다. 3개의 서로 다른 매질, 4개의 서로 다른 전리함 및 전기계 조합에 따른 12 가지 측정조건에 대한 흡수선량의 변화는 평균 0.6％의 차이를 보여 주였으며 임의의 전리함 및 전기계 조합에 대하여 물팬텀 및 고체물팬텀에 대한 TG21, MEA 측정법에 의한 흡수선량비의 변화 양상이 같은 양상을 보여주고 있으나 그 차이가 평균 1.96％를 보임으로서 고체물팬텀이 절대 흡수선량 측정에는 적절치 않은 것으로 사료된다. TG21 측정법에 따른 물팬텀과 폴리스틸렌팬텀을 이용한 절대 흡수선량값이 1.54％의 차이를 보임으로서 팬텀 매질에 대한 비교 factor가 필요할 것으로 사료된다. 측정매질, 전리함, 전기계 등의 여러 조건에 대한 흡수선량값의 차이가 TG21, IAEA 프로토콜에서 1％ 이내의 차이를 보여 주고 있으며 상대적인 변화 양상이 측정법에 상관없이 같은 경향으로 변함으로서 측정조건이 측정법에 영향을 주지 않았음을 알 수 있다. 다만 표준 측정법을 사용할 때 팬텀에 의한 차이는 많이 날 수 있으므로 측정법에서 사용하는 표준 팬텀을 사용 할 것을 권장하며 이것이 어려운 경우는 병원에서 사용하는 팬텀에 대한 보정값을 자체적으로 구하여 사용하는 것이 오차를 줄일 수 있을 것으로 사료된다.

• Journal of Radiation Protection and Research
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• 제9권1호
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• pp.19-25
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• 1984

There is not yet an universal method of electron dosimetry. The Authors measured dose distributions of the electron beams from Clinac-18 by means of silicon detector connected to X-Y recorder, and compared them in water phantom with dose distributions measured by film and ion chamber, both inserted in polystyrene phantom. The results are as followings, 1. Dose in build-up region increased with the field size for all energy, and depth dose profiles of $6{\sim}12MeV$ beam under the depth of maximum dose were independent of field size, but those of 15 and 18 MeV beam were dependent on the field size. 2. The widths of penumbra by semiconductor detector were narrower than those by film for same energy beam. 3. Depth dose profiles by three different dosimeter did not coincide each other. In the build-up region, dose by semiconductor detector was lower than that by any other dosimeter.

• 대한방사선치료학회지
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• 제9권1호
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• pp.40-45
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• 1997

When therapeutic irradiation is indicated for the orbital tumors, the greatest concern is the risk of radiation-induced cataract. Conjunctival lymphoma is one of the good examples. We would like to report the procedure of the lens shielding device(L.S.D) and the result of irradiated dose to the lens. L.S.D. consistes of two parts : load alloy to attenuate electron beam, and dental acryl which completely covers the lead alloy to avoid discomfort of cornea from contacting directly with cerrobend and side scattering by cerrobend. And for easy location and removal, side bars were made on each side. Radiation doses were meaured with TLD(TLD 3500 Hawshaw). Markus chamber in a polystyrene phantom. The phantom was irradiated with 9MeV electron beams from Clinac 2100C with $6{\times}6cm$ electron cone. The relative dose at 6mm depth where the lens is located was $4.2\%$ with TLD and $5.1\%$ with Markus chamber clinically when 2600 cGy are irradiated to the eyeball, the mapinary dose to the lens will be 109 cGy or 132 cGy, which will significently reduce the cataract.

• Radiation Oncology Journal
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• 제1권1호
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• pp.41-45
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• 1983

To obtain 7 MeV electron beam which is suitable for treatment of the chest wall after radical of modified radical mastectomy, the authors reduced the energy of electron beam by means by Lucite plate inserted in the beam. To determine the proper thickness of the Lucite plate necessary to reduce the energy of 9 MeV electron beam to 6 MeV, dosimetry was made by using a parallel plate ionization chamber in polystyrene phantom. Separation between two adjacent fields, 7 MeV for chest wall and 12 MeV for internal mammary region, was studied by means of film dosimetry in both polytyrene phantom and Humanoid phantom. The results were as follows. 1. The average energy of 9 MeV electron beam transmitted through the Lucite plate was reduced. Reduction was proportional to the thickness of the Lucite plate in the rate of 1.7 MeV/cm. 2. The proper thickness of the Lucite plate necessary to obtain 6 MeV electron beam from 9 MeV was 1.2 cm. 3. 7 MeV electron beam, 80% dose at 2cm depth, is adequate for treatment of the chest wall. 4. Proper separation between two adjacent electron fields, 7 MeV and 12 MeV, was 5mm on both flat surface and sloping surface to produce uniform dose distribution.