• Title/Summary/Keyword: photon beam

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Dose distribution at junctional area for head and neck radiotherapy (두경부 방사선치료시 접합 조사면의 선량분포)

  • 김정기;김기환;오영기;김진기;정동혁;신교철;양광모;조문준;박인규
    • Progress in Medical Physics
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    • v.12 no.2
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    • pp.161-169
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    • 2001
  • For the head and neck radiotherapy, the technique of half beam using independent collimator is very useful to avoid overlapping of fields particularly when the lateral neck fields are placed adjacent to anterior supraclavicular field. Also abutting photon field with electron field is frequently used for the irradiation of posterior neck when tolerable dose on spinal cord has been reached. Using 6 MV X-ray and 9 MeV electron beams of Clinac1800(Varian, USA) linear accelerator, we performed film dosimetry by the X-OMAT V film of Kodak in solid water phantom and the dose distribution at beam center of 2 half beams further examined according to depths(0 cm, 1.5 cm, 3 cm, 5 cm) for single anterior half beam and anterior/posterior half beam. The dose distribution to the junction line between photon and electron fields was also measured. For the single anterior half beam, the absorption doses at 0.3 cm, 0.5 cm and 1 cm distances from beam center were 88%, 93% and 95% of open beam, respectively. In the anterior/posterior half beams, the absorption doses at 0.3 cm, 0.5 cm and 1 cm distances from beam center were 92%, 93% and 95% of open beam, respectively At the junction line between photon and electron fields, hot spot was developed on the side of the photon field and a cold spot was developed on that of the electron field. The hot spot in the photon side was developed at depth 1.5 cm with 7 mm width. The maximum dose of hot spot was increased to 6% of reference doses in the photon field. The cold spot in the electron side was developed at all measured depths(0.5 cm-3 cm) with 1-12.5 mm widths. The decreased dose in the cold spot was 4.5-30% of reference dose in the electron field. With above results, we concluded that when using electron beam or independent jaw for head and neck radiotherapy, the hot and cold dose area should be considered as critical point.

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Characteristics of 23 MV Photon Beam from a Mevatron KD 8067 Dual Energy Linear Accelerator (Mevatron KD 8067 선형가속기의 23 MV 광자선의 특성)

  • Kim, Ok-Bae;Choi, Tae-Jin;Kim, Young-Hoon
    • Radiation Oncology Journal
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    • v.8 no.1
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    • pp.115-124
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    • 1990
  • The characteristics of 23 MV photon beam have been presented with respect to clinical parameters of central axis depth dose, tissue-maxi mum ratios, scatter-maximum ratios, surface dose and scatter correction factors. The nominal accelerating potential was found to be $18.5\pm0.5$ MV on the central axis. The half-value layer (HVL) of this photon beam was measured with narrow beam geometry from central axis, and it has been showed the thickness of $24.5\;g/cm^2$. The tissue-maximum ratio values have been determined from measured percentage depth dose data. In our experimental dosimetry, the surface dose of maximum showed only $9.6\%$ of maximum dose at $10\times10\;cm^2$, 100 cm SSD, without blocking tray in. The TMR'S of $0\times0$ field size have been determined to get average $2.3\%$ uncertainties from three different methodis; are zero effective attenuation coefficient, non-ilnear least square fit of TMR's data and effective linear attenuation coefficient from the HVL of 23 MV photon beams of dual energy linear accelerator.

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Radiochromic film dosimetry for linac-based stereotactic radiosurgery

  • Han, Seung-Hee;Park, Suk-Won;Oh, Do-Hoon
    • Proceedings of the Korean Society of Medical Physics Conference
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    • 2002.09a
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    • pp.302-304
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    • 2002
  • In linac-based stereotactic radiosurgery, assuring the quality of the planning and delivery of external photon beam requires accurate evaluation of beam parameters, usually including output factors, tissue-phantom ratio and off-axis ratios, and measurement of actual dose distributions from simulated treatment. We're going to test the use of calibrated radio chromic film (Gafchromic film; type MD-55, Nuclear associate) using a Lumiscan 75 digitizer to measure absolute dose and relative dose distributions for linac-based radiosurgery unit Relative dose distribution of a human-style spherical acryl phantom were measured using radiochromic film and calculated by treatment planning system. The absolute dose at the sphere center was measured by radiochromic film and micro chamber (Exradin A-14, 0.009cc). What we want to demonstrate in this work, the 'well selected' radiochromic films when external photon beam are used in linac-based stereotactic radiosurgery are very accurate detector for dosimetry.

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Effect of Target Angle and Thickness on the Heel Effect and X-ray Intensity Characteristics for 70 kV X-ray Tube Target

  • Kim, Gyehong;Lee, Rena
    • Progress in Medical Physics
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    • v.27 no.4
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    • pp.272-276
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    • 2016
  • To investigate the optimum x-ray tube design for the dental radiology, factors affecting x-ray beam characteristics such as tungsten target thickness and anode angle were evaluated. Another goal of the study was to addresses the anode heel effect and off-axis spectra for different target angles. MCNPX has been utilized to simulate the diagnostic x-ray tube with the aim of predicting optimum target angle and angular distribution of x-ray intensity around the x-ray target. For simulation of x-ray spectra, MCNPX was run in photon and electron using default values for PHYS:P and PHYS:E cards to enable full electron and photon transport. The x-ray tube consists of an evacuated 1 mm alumina envelope containing a tungsten anode embedded in a copper part. The envelope is encased in lead shield with an opening window. MCNPX simulations were run for x-ray tube potentials of 70 kV. A monoenergetic electron source at the distance of 2 cm from the anode surface was considered. The electron beam diameter was 0.3 mm striking on the focal spot. In this work, the optimum thickness of tungsten target was $3{\mu}m$ for the 70 kV electron potential. To determine the angle with the highest photon intensity per initial electron striking on the target, the x-ray intensity per initial electron was calculated for different tungsten target angles. The optimum anode angle based only on x-ray beam flatness was 35 degree. It should be mentioned that there is a considerable trade-off between anode angle which determines the focal spot size and geometric penumbra. The optimized thickness of a target material was calculated to maximize the x-ray intensity produced from a tungsten target materials for a 70 keV electron energy. Our results also showed that the anode angle has an influencing effect on heel effect and beam intensity across the beam.

The Measurements of Energy and Distribution of Scattered Electrons in Therapeutic X-Ray Beam (치료 방사선 선속(Flux)에 포함된 산란전자의 분포와 에너지 측정)

  • Vahc, Young-Woo;Park, Kyung-Ran;Ohyun Kwon;Lee, Yong-Ha;Kim, Tae-Hong;Kim, Sookil
    • Progress in Medical Physics
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    • v.13 no.1
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    • pp.1-8
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    • 2002
  • Accurate knowledge of the distribution of contamination electrons ( which comes from mainly gantry head by Compton scattering, pair production, and tray: henceforth called leptons ) at the surface and in the first centimeters of tissue is essential for the clinical practice of radiation oncology. Such lepton tends to reduce or eliminate the ‘skin-sparing’ advantage of megavoltage photon beam radiotherapy, This information is needed to prescribe a absorbed dose to a skin volume at a few millimeter depth in high energy therapeutic radiation photon beam All experiments were done with 15 MV photon beam from a dual energy linear accelerator (Clinac 1800, Varian). Field size is defined by ranged from 10.0$\times$10.0 to 30.0$\times$30.0 $\textrm{cm}^2$. The absorbed dose and distribution of leptons in therapeutic radiation beam (15 MV) are investigated by means of variable blocked beams of 30.0$\times$30.0 $\textrm{cm}^2$ and dose beam profiles partly removed leptons with a copper plate. A numerous leptons mainly are distributed as shape of broad cone in the central photon beam and leptons path length in the water are shorter than 2.5 cm because of the leptons energy having around 3.0 MeV. These results clearly appears that the subtraction of leptons from the total depth dose curve not only lower the absolute dose in the buildup region and surface dose, it also causes a shift of d$_{max}$ to a deeper depth.

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Monte Carlo Simulation for Electron Contamination of Photon Beam (치료용 광자선의 전자오염에 대한 몬테카를로 시뮬레이션)

  • Chung, Kap-Soo;Ko, Shin-Kwan;Yang, Han-Joon;Han, Chang-Yul
    • Journal of radiological science and technology
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    • v.22 no.2
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    • pp.47-51
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    • 1999
  • We calculated the energy distribution and the percentage depth-dose at 10 cm in a $10{\times}10\;cm^2$ with a photon beam at SSD of 100 cm by using a Monte Carlo Simulation. PDD is used as a beam-quality specifier for radiotherapy beams. It is better than the commonly used values of TPR or nominal accelerating potential. The presence of electron contamination affects the measurement of PDD, but can be removed by the use of a 0.1 cm lead filter. It reduces surface dose from contaminant electrons from the accelerator by more than 90% for radiotherapy beams. The filter performs best when it is placed immediately below the head. An electron-contamination correction factor is introduced to correct for electron contamination from the filter and air. It converts PDD which includes the electron contamination with the filter in place into PDD for the photons in the filtered beam. The correction factor can be used to determine stopping-power ratio. Calculations show that the values of water-to-air slopping power ratio in the unfiltered beam are related to PDD.

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The Variation of Surface Dose by Beam Spoiler in 10 MV Photon Beam from Linear Accelerator (선형가속기 10 MV 광자선에서 산란판(Beam Spoiler) 사용 시 표면선량 변화)

  • Bae, Seong-Cheol;Kim, Jun-Ho;Lee, Choul-Soo
    • The Journal of Korean Society for Radiation Therapy
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    • v.18 no.1
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    • pp.21-28
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    • 2006
  • Purpose: The purpose of this study is to find a optimal beam spoiler condition on the dose distribution near the surface, when treating a squamous cell carcinoma of the head and neck and a lymphatic region with 10 MV photon beam. The use of a optimal spoiler allows elivering high dose to a superficial tumor volume, while maintaining the skin-sparing effect in the area between the surface to the depth of 0.4 cm. Materials and Methods: The lucite beam spoiler, which were a tissue equivalent, were made and placed between the surface and the photon collimators of linear accelerator. The surface-dose, the dose at the depth of 0.4 cm, and the maximum dose at the dmax were measured with a parallel-plate ionization chamber for $5{\times}5cm\;to\;30{\times}30cm^2$ field sizes using lucite spoilers with different thicknesses at varying skin-to-spoiler separation (SSS). In the same condition, the dose was measured with bolus and compared with beam spoiler. Results: The spoiler increased the surface and build-up dose and shifted the depth of maximum dose toward the surface. With a 10 MV x-ray beam and a optimal beam spoiler when treating a patient, a similer build-up dose with a 6 MV photon beam could be achieved, while maintaining a certain amount of skin spring. But it was provided higher surface dose under SSS of less than 5 cm, the spoiler thickness of more than 1.8 cm or more, and larger field size than $20{\times}20cm^2$ provided higher surface dose like bolus and obliterated the spin-sparing effect. the effects of the beam spoiler on beam profile was reduced with increasing depths. Conclusion: The lucite spoiler allowed using of a 10 MV photon beam for the radiation treatment of head and neck caner by yielding secondary scattered electron on the surface. The dose at superficial depth was increased and the depth of maximum dose was moved to near the skin surface. Spoiling the 10 MV x-ray beam resulted in treatment plans that maintained dose homogeneity without the consequence of increased skin reaction or treat volume underdose for regions near the skin surface. In this, the optimal spoiler thickeness of 1.2 cm and 1.8 cm were found at SSS of 7 cm for $10{\times}10cm^2$ field. The surface doses were measured 60% and 64% respectively. In addition, It showed so optimal that 94% and 94% at the depth of 0.4 cm and dmax respectively.

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6MV Photon Beam Commissioning in Varian 2300C/D with BEAM/EGS4 Monte Carlo Code

  • Kim, Sangroh;Jason W. Sohn;Cho, Byung-Chul;Suh, Tae-Suk;Choe, Bo-Yong;Lee, Hyoung-Koo
    • Proceedings of the Korean Society of Medical Physics Conference
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    • 2002.09a
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    • pp.113-115
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    • 2002
  • The Monte Carlo simulation method is a numerical solution to a problem that models objects interacting with other objects or their environment based upon simple object-object or object-environment relationships. In spite of its great accuracy, It was turned away because of long calculation time to simulate a model. But, it is used to simulate a linear accelerator frequently with the advance of computer technology. To simulate linear accelerator in Monte Carlo simulations, there are many parameters needed to input to Monte Carlo code. These data can be supported by a linear accelerator manufacturer. Although the model of a linear accelerator is the same, a different characteristic property can be found. Thus, we performed a commissioning process of 6MV photon beam in Varian 2300C/D model with BEAM/EGS4 Monte Carlo code. The head geometry data were put into BEAM/EGS4 data. The mean energy and energy spread of the electron beam incident on the target were varied to match Monte Carlo simulations to measurements. TLDs (thermoluminescent dosimeter) and radiochromic films were employed to measure the absorbed dose in a water phantom. Beam profile was obtained in 40cm${\times}$40cm field size and Depth dose was in 10cm${\times}$10cm. At first, we compared the depth dose between measurements and Monte Carlo simulations varying the mean energy of an incident electron beam. Then, we compared the beam profile with adjusting the beam radius of the incident electron beam in Monte Carlo simulation. The results were found that the optimal mean energy was 6MV and beam radius of 0.1mm was well matched to measurements.

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Development of Laser-driven Proton Source Toward Its Applications

  • Sagisaka, Akito;Daido, Hiroyuki;Pirozhkov, Alexander S.;Yogo, Akifumi;Ogura, Koichi;Orimo, Satoshi;Ma, Jinglong;Mori, Michiaki;Nishiuchi, Mamiko;Bulanov, Sergei V.;Esirkepov, Timur Zh.;Oishi, Yuji;Nayuki, Takuya;Fujii, Takashi;Nemoto, Koshichi;Nagatomo, Hideo
    • Journal of the Optical Society of Korea
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    • v.13 no.1
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    • pp.37-41
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    • 2009
  • We observe the proton signals produced by laser interaction with thin-foil targets of polyimide and of copper. We change the thickness of the polyimide target to $7.5{\mu}m$, $12.5{\mu}m$, and $50{\mu}m$. High-energy protons with the maximum energy of ${\sim}2.3\;MeV$ from $7.5{\mu}m$ thick polyimide are observed. This proton beam with the maximum energy of multi-MeV has various applications such as a proton shadowgraphy.