• 한국의학물리학회지:의학물리
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• 제25권1호
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• pp.37-45
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• 2014

ConeBeam Computed Tomography (CBCT) 영상을 기반으로 한 선량계산에서는 Fanbeam Computed Tomography (FBCT)와 비교하여 산란에 의한 영향이 크고 그 양상이 다양하게 나타나 오차의 주요한 요인으로 작용하는 것으로 알려져 있다. 본 논문에서는 골반 방사선 치료에서 산란이 CBCT 기반으로 한 선량계산에 미치는 영향을 평가하여 오차를 최소화 할 수 있는 조건에 대하여 연구하였다. 다양한 산란조건에서의 CBCT 영상 취득을 위하여 전자밀도 교정용 팬텀에 크기가 각기 다른 산란물질을 추가하여 "산란부족", "산란과다", 그리고 "산란충분"의 3가지 조건을 정하였다. 산란조건에서 취득된 CBCT 영상에서 팬텀 중심부와 주변부의 위치에 따른 CT number값의 차이와 분포를 분석하여 균질도를 평가하였으며 FBCT 영상 기반의 선량 분포를 기준으로 하여 다양한 산란조건에서의 전자밀도 교정관계를 적용하였을 때 팬텀 및 전립선암 환자 5명의 CBCT 영상에서 계산된 선량분포의 감마합격률 및 상대적 오차를 구하였다. 팬텀 CBCT 영상에 대한 CT number들의 히스토그램에서의 분포에서 물 등가 물질에 해당하는 피크의 폭(FWHM)은 산란부족(685 HU)이나 산란과다(264 HU)보다 산란충분(146 HU)의 조건에서 가장 작게 나타나 균질도가 제일 좋은 것으로 평가되었고 팬텀의 중심부와 주변부에서 동일 성분에 대한 CT number의 차이 역시 같은 결과를 나타내었다. 또한 팬텀의 CBCT 영상을 취득할 때와 동일한 산란조건에서의 교정조건을 적용한 경우 선량계산이 가장 정확하였으며 산란충분의 교정곡선 조건을 적용하였을 때 5명의 전립선암환자(평균 등가지름 27.2 cm)의 CBCT 영상 기반의 선량분포는 FBCT의 경우와 대비하여 1%/3 mm의 감마지표에서 감마합격률 98% 이상을 나타내었다. 이때 FBCT 선량에 대한 CBCT 선량오차는 처방선량 대비 2% 이하(평균 0.2%, -1.3%~1.6%)로 평가되었다. CBCT 골반 촬영을 할 때 일반적인 성인 골반의 원통 등가지름(ECD, Equivalent Cylindrical Diameter)의 산란조건에서 동일 성분에 대한 HU 값이 가장 균질하게 나타나 골반 촬영모드가 최적화되었음을 확인하였으며 일반적인 골반부위와 ECD가 유사한 산란조건, 즉 산란충분조건에서 취득된 전자밀도 교정관계를 적용하여 골반 CBCT 기반에서 선량을 계산하였을 때 최적의 선량 정확성을 확보할 수 있었다.

• 한국의학물리학회지:의학물리
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• 제28권1호
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• pp.33-38
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• 2017

Creating individualized build-up material for superficial photon beam radiation therapy at irregular surface is complex with rice or commonly used flat shape bolus. In this study, we implemented a workflow using 3D printed patient specific bolus and describe our clinical experience. To provide better fitted build-up to irregular surface, the 3D printing technique was used. The PolyLactic Acid (PLA) which processed with nontoxic plant component was used for 3D printer filament material for clinical usage. The 3D printed bolus was designed using virtual bolus structure delineated on patient CT images. Dose distributions were generated from treatment plan for bolus assigned uniform relative electron density and bolus using relative electron density from CT image and compared to evaluate the inhomogeneity effect of bolus material. Pretreatment QA is performed to verify the relative electron density applied to bolus structure by gamma analysis. As an in-vivo dosimetry, Optically Stimulated Luminescent Dosimeters (OSLD) are used to measure the skin dose. The plan comparison result shows that discrepancies between the virtual bolus plan and printed bolus plan are negligible. (0.3% maximum dose difference and 0.2% mean dose difference). The dose distribution is evaluated with gamma method (2%, 2 mm) at the center of GTV and the passing rate was 99.6%. The OSLD measurement shows 0.3% to 2.1% higher than expected dose at patient treatment lesion. In this study, we treated Mycosis fungoides patient with patient specific bolus using 3D printing technique. The accuracy of treatment plan was verified by pretreatment QA and in-vivo dosimetry. The QA results and 4 month follow up result shows the radiation treatment using 3D printing bolus is feasible to treat irregular patient skin.

• 한국환경성돌연변이발암원학회지
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• 제15권2호
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• pp.122-130
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• 1995

In order to evaluate the cytotoxicity of lead in cultures of Balb/c mouse 3T3 cell line, various cytotoxic assays were carried out after expose cells to various concentrations of lead nitrate. Cytotoxic assays using this study were included NR assay, MTT assay, measurement of LDH and protein, synthetic rate of DNA and UDS. Intrace!!ular Ca$^{2+}$ level was also measured. Light and electron microscopic studies were done for morphological changes of lead-treated cell cultures. The results were as follows; 1. The absorbances of NR and MTT were decreased dose-dependently, and NR, and MTT, values of lead nitrate were 3.4 mM and 1.5 mM, respectively. 2. Amount of LDH released into the medium was increased in dose-dependently and LDH activity at 5 mM concentration of lead nitrate was increased to 335 % of control. 3. Amount of total protein was decreased dose-dependently, and which was half of control at 2 mM concentration of lead nitrate. 4. The synthetic rate of DNA was decreased dose-dependently, and also which was remarkably decreased at 3 mM and 5 mM concentrations of lead nitrate. 5. The synthetic rate of UDS was increased at 1 mM concentration of lead nitrate, but which was remarkably decreased at 3 mM and 5 mM concentrations of lead nitrate. 6. Intrace!lular Ca$^{2+}$ level was remarkably increased at 1 mM concentration of lead nitrate, compared with control. 7. In light microscopy, number of cells and processes were decreased according to the increase of dosage of lead nitrate. Electron microscopic findings showed that many vacuoles and cisternal dilatation of rough endoplasmic reticulum were seen in the cytoplasm at 1 mM concentration of lead nittale. From the above results, high dosage treatment of lead nitrate (>3 mM) damaged genetic malerials and it also showed cytotoxicity in mouse 3T3 cell line cultures by injury of cell organelles and Ca$^{2+}$ channel.

• 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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• 제8권1호
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• pp.41-54
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• 1996

The secondary electrons developed by interaction between primary beam and a tray mounted for blocks in Megavoltage irradiation result in excess soft radiation dose to the surface layer. To reduce this electron contamination, electron filters have been used to be attached under a tray. Various filters with Cu and Al plates in six different thickness and Cu/Al combined plates in 3 different thickness were tested to measure the reduction rate of secondary electron contamination to the surface layer. The measurement to find optimal filter was performed on 6MV linear accelerator in $10 cm{\times}10 cm$ field size and fixed 78.5cm source to measurement points distance from surface to maximum build up point in 2mm intervals. The result was analyzed as the ratio of measured doses with using filters, to standard doses of measured open beam. The result of this study was fellowing : 1. The contaminated low energy radiation were mainly produced by blocking tray. 2. The surface absorbed dose was slowly increased by increasing irradiation field size but rapidly increased at field size above $15cm{\times}15cm$. 3. Al plate upto 2.5mm thickness used as a filter was found to be inadequate due to the failure of reduction of the surface absorbed dose below doses of the under surface upto the maximal build up. Cu 0.5mm plate and Cu 0.28mm/A1 1.5mm compound plate were found to be optimal filters. 4. By using these 2 filters, the absorbed dose to the surface were effectively reduced $5.5\%$ in field size $4cm{\times}4cm,\;11.3\%$ in field size $10cm{\times}10cm,\;22.3\%$ in field size $25cm{\times}25cm$. 5. In field size $10cm{\times}10cm$, the absorbed dose to the surface of irradiation was reduced by setting TSD 20cm at least,. but effective and enough dose reduction could be achieved by setting TSD 30cm as 2 optimal filters used. 6. More surface dose absorbed at TSD less than 7.4cm with a tray and filters together indicated that soft radiation was also developed by filters. 7. The variation of PDD by the different size of irradiation field was minimal as 2 optimal filters used. There was also not different in variation of PDD according to using any of two different filters. 8. PDD was not effected either by various TSD or by using the different filter among two.

• 치과방사선
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• 제18권1호
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• pp.137-147
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• 1988

This study was designed to investigate the effects of irradiation on the salivary ductal cells, especially on the intercalated ductal cells of the rat parotid glands. For this study, 36 Sprague-Dawley strain rats were irradiated on the head and neck region with absorbed dose of 15Gy by Co-60 teletherapy unit, Picker's model 4M60. The conditions irradiated were that field size, SSD, dose rate and depth were 12×5㎝m, 50㎝, 222 Gy/min. and 1㎝. respectively. The experimental animals were sacrificed 1, 2, 3, 6, 12 hours and 1, 3, 7 days after the irradiation and the changes of the irradiated intercalated duct cells of the parotid glands were examined under the light and electron microscope. The results were as follows: 1. Under the light and electron microscope, the nucleus, mitochondria and secretory granules showed severe changes in the early stage after irradiation and the most severe cellular de- generations were observed 2 hours after irradiation, but the repair processes began from 6 hours after irradiation. 2. Under the electron microscope, loss of the nuclear membranes, derrangement of the chromosomes, swelling and destruction of the secretory granules, and widening of the intercellular spaces were observed after irradiation. 3. Under the light microscope, atrophy and irregular proliferation of the ductal cells, cuboidal metaplasia, hyperchromatism, and the construction or obstruction of the lumen were observed after irradiation.

• 한국의학물리학회지:의학물리
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• 제11권2호
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• pp.147-155
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• 2000

Patient dose verification is one of the most important parts in quality assurance of the treatment delivery for radiation therapy. The dose distributions may be meaningfully improved by modulating two dimensional intensity profile of the individual high energy radiation beams In this study, a new method is presented for the pre-treatment dosimetric verification of these two dimensional distributions of beam intensity by means of a charge coupled device video camera-based fluoroscopic device (henceforth called as CCD-VCFD) as a radiation detecter with a custom-made software for dose calculation from fluorescence signals. This system of dosimeter (CCD-VCFD) could reproduce three dimensional (3D) relative dose distribution from the digitized fluoroscopic signals for small (1.0$\times$1.0 cm$^2$ square, ø 1.0 cm circular ) and large (30$\times$30cm$^2$) field sizes used in intensity modulated radiation therapy (IMRT). For the small beam sizes of photon and electron, the calculations are performed In absolute beam fluence profiles which are usually used for calculation of the patient dose distribution. The good linearity with respect to the absorbed dose, independence of dose rate, and three dimensional profiles of small beams using the CCD-VCFD were demonstrated by relative measurements in high energy Photon (15 MV) and electron (9 MeV) beams. These measurements of beam profiles with CCD-VCFD show good agreement with those with other dosimeters such as utramicro-cylindrical (UC) ionization chamber and radiographic film. The study of the radiation dosimetric technique using CCD-VCFD may provide a fast and accurate pre-treatment verification tool for the small beam used in stereotactic radiosurgery (SRS) and can be used for verification of dose distribution from dynamic multi-leaf collimation system (DMLC).

• 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.

• 한국의학물리학회지:의학물리
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• 제27권1호
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• pp.25-30
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• 2016

본 연구에서는 의료용 선형가속기 제작을 위해 개발된 연구용 선형가속기의 전자선에 대한 선량학적 특성을 실험적으로 평가하였다. 본 논문에서는 전자총 가열 전류에 따른 에너지의 변화와 출력 흡수선량 측정 결과를 보고하고자 한다. 전자선의 에너지는 필름 측정법을 써서 평균에너지와 최빈에너지의 관점에서 결정하였다. 출력 흡수선량은 최적 에너지에 대하여 평행평판형 전리함을 사용하여 물속 깊이선량율을 측정하고 TRS-398 프로토콜에 따라 결정하였다. 측정 결과 전자총 가열 전류 2.02~2.50 A에서 평균에너지와 최빈에너지는 5.94~2.80 MeV와 6.54~3.31 MeV로 변화하였다. 그리고 평균에너지 5.94 MeV의 전자선에 대해 물속 기준 깊이에서 출력 흡수선량은 5.41 Gy/min으로 나타났다.

• 한국콘텐츠학회논문지
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• 제14권2호
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• pp.457-466
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• 2014

고 에너지 전자선 치료에 있어서 차폐물질은 종양조직 외 정상조직이나 주요장기를 보호하기 위해 사용된다. 하지만 이러한 물질에서 발생되어지는 산란선은 심부선량에 영향을 줄 수 있으며, 물질원자번호에 따라 다르게 나타난다. 이에 차폐물질로써 사용가능한 알루미늄, 구리, 납 등의 다양한 원자번호 물질을 전하 감약율 95% 되는 두께로 하여 측정과 MCNPX 모의계산으로 산란율을 비교분석하였다. 산란선 영향을 많이 받는 표면의 선량변화율은 최대 물질두께에서 +0.88%, 원자번호에서 +0.43%의 영향을 받으며, 전하 감약율 95% 되는 두께의 알루미늄, 구리, 납 물질은 측정에서 +19.70%, +15.20%, +12.40% 계산에서 +25.00%, +15.10%, +13.70%를 보였다. 이로 인해 산란율은 물질두께가 원자번호보다 많은 영향을 주며, 산란전자가 광자보다 많은 기여를 하고 있음을 알 수 있었다. 이에 임상에서의 적절한 차폐물질은 두께영향 산란선이 적게 방출되는 고 원자번호물질이 적당하다고 사료된다.