• Title/Summary/Keyword: Depth Dose

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Peripheral Dose Distributions of Clinical Photon Beams (광자선에 의한 민조사면 경계영역의 선량분포)

  • 김진기;김정수;권형철
    • Progress in Medical Physics
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    • v.12 no.1
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    • pp.71-77
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    • 2001
  • The region, near the edge of a radiation beam, where the dose changes rapidly according to the distance from the beam axis is known as the penumbra. There is a sharp dose gradient zone even in megavoltage photon beams due to source size, collimator, lead alloy block, other accessories, and internal scatter ray. We investigate dosimetric characteristics on penumbra regions of a standard collimator and compare to those of theoritical model for the optimal use of the system in radiotherapy. Peripheral dose distribution of 6 W Photon beams represents penumbral forming function as the depth. Also we have discussed that the peripheral dose distribution of clinical photon beams, differences between calculation dose use of emperical penumbral forming function and measurements in penumbral region. Predictions by emperical penumbral forming functions are compared with measurements in 3-dimensional water phantom and it is shown that the method is capable of reproduceing the measured peripheral dose values usually to within the statistical uncertainties of the data. The semiconductor detector and ion chamber were positioned at a dmax depth, 5cm depth, 10cm depth, and its specific ratio was determined using a scanning data. The effective penumbra, the distance from 80% to 20% isodose lines were analyzed as a function of the distance. The extent of penumbra will also expand with depth increase. Difference of measurement value and model functions value according to character of the detector show small error in dose distribution of the peripheral dose.

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Performance Evaluation of Stealth Chamber as a Novel Reference Chamber for Measuring Percentage Depth Dose and Profile of VitalBeam Linear Accelerator (VitalBeam 선형가속기의 심부선량백분율과 측방선량분포 측정을 위한 새로운 기준 전리함으로서 스텔스 전리함의 성능 평가)

  • Kim, Yon-Lae;Chung, Jin-Beom;Kang, Seong-Hee;Kang, Sang-Won;Kim, Kyeong-Hyeon;Jung, Jae-Yong;Shin, Young-Joo;Suh, Tae-Suk;Lee, Jeong-Woo
    • Journal of radiological science and technology
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    • v.41 no.3
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    • pp.201-207
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    • 2018
  • The purpose of this study is to evaluate the performance of a "stealth chamber" as a novel reference chamber for measuring percentage depth dose (PDD) and profile of 6, 8 and 10 MV photon energies. The PDD curves and dose profiles with fields ranging from $3{\times}3$ to $25{\times}25cm^2$ were acquired from measurements by using the stealth chamber and CC 13 chamber as reference chamber. All measurements were performed with Varian VitalBeam linear accelerator. In order to assess the performance of stealth chamber, PDD curves and profiles measured with stealth chamber were compared with measurement data using CC13 chamber. For PPDs measured with both chambers, the dosimetric parameters such as $d_{max}$ (depth of maximum dose), $D_{50}$ (PDD at 50 mm depth), and $D_{100}$ (PDD at 100 mm depth) were analyzed. Moreover, root mean square error (RMSE) values for profiles at $d_{max}$ and 100 mm depth were evaluated. The measured PDDs and profiles between the stealth chamber and CC13 chamber as reference detector had almost comparable. For PDDs, the evaluated dosimetric parameters were observed small difference (<1%) for all energies and field sizes, except for $d_{max}$ less than 2 mm. In addition, the difference of RMSEs for profiles at $d_{max}$ and 100 mm depth was similar for both chambers. This study confirmed that the use of stealth chamber for measuring commission beam data is a feasible as reference chamber for fields ranging from $3{\times}3$ to $20{\times}20cm^2$. Furthermore, it has an advantage with respect to measurement of the small fields (less than $3{\times}3cm^2$ field) although not performed in this study.

Effect of an Acrylic Plate and SSD on Dose Profile and Depth Dose Distribution of 9 MeV Electron Beams (에너지 저하체로서 아크릴과 SSD 가 9MeV 전자선의 측방 및 깊이선량분포에 미치는 효과)

  • 강위생
    • Progress in Medical Physics
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    • v.9 no.2
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    • pp.65-71
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    • 1998
  • The aims are to evaluate the effects of an 1.0 cm acrylic plate and SSD on the dose profile and depth dose distribution of 9 MeV electron beam and to analyse adequacy for using an acrylic plate to reduce energy of electron beams. An acrylic plate of 1.0 cm thickness was used to reduce energy of 9 MeV electron beam to 7 MeV. The plate was put on an electron applicator at 65.4 cm distance from x-ray target. The size of the applicator was 10${\times}$l0cm at 100 cm SSD. For 100cm, l05cm and 110cm SSD, depth dose on beam axis and dose profiles at d$\_$max/ on two principal axes were measured using a 3D water phantom. From depth dose distributions, d$\_$max/, d$\_$85/, d$\_$50/ and R$\_$p/, surface dose, and mean energy and peak energy at surface were compared. From dose profiles flatness, penumbra width and actual field size were compared. For comparison, 9 MeV electron beams were measured. Surface dose of 7 MeV electron beams was changed from 85.5% to 82.2% increasing SSD from 100 cm to 110 cm, and except for dose buildup region, depth dose distributions were independent of SSD. Flatness of 7 MeV ranged from 4.7% to 10.4% increasing SSD, comparing 1.4% to 3.5% for 9 MeV. Penumbra width of 7 MeV ranged from 1.52 cm to 3.03 cm, comparing 1.14 cm to 1.63 cm for 9 MeV. Actual field size increased from 10.75 cm to 12.85 cm with SSD, comparing 10.32 cm to 11.46 cm for 9 MeV. Virtual SSD's of 7 and 9 MeV were respectively 49.8 cm and 88.5cm. In using energy reducer in electron therapy, depth dose distribution were independent of SSD except for buildup region as well as open field. In case of using energy reducer, increasing SSD made flatness to deteriorate more severely, penumbra width more wide, field size to increase more rapidly and virtual SSD more short comparing with original electron beam. In conclusion, it is desirable to use no energy reducer for electron beam, especially for long SSD.

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A Study on the Tendency of Dose value According to Dose calibrator Measurement Depth and Volume (Dose calibrator 측정 깊이와 용량의 변화에 따른 선량 값의 성향에 대한 고찰)

  • Kim, Jin Gu;Ham, Jun Cheol;Oh, Shin Hyun;Kang, Chun Koo;Kim, Jae Sam
    • The Korean Journal of Nuclear Medicine Technology
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    • v.24 no.1
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    • pp.20-26
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    • 2020
  • Purpose It is intended to figure out the errors derived from changes in depth and volume when measuring the Standard source and 99mTc-pertechnetate by using a Dose calibrator. Then recommend appropriate measurement depth and volume. Materials and Methods As a Dose calibrator, CRC-15βeta and CRC-15R (Capintec, New Jersey, USA) was used, and the measurement sources were 57Co, 133Ba, 137Cs and 99mTc-pertechnetate was also adopted due to its high frequency of use. The Standard source was respectively measured the changes according to its depth without changing the volume, in a range of 0 cm to 15 cm from the bottom of the ion chamber. 99mTc-pertechnetate was measured at each depth by changing the volume with 0.1 mL, 0.3 mL, 0.5 mL, 0.7 mL and 0.9 mL Respectively. And the depth range was from 0 cm to 15 cm at the bottom of the ion chamber. Results In the case of Standard source 57Co, 133Ba, 137Cs and 99mTc-pertechnetate, there were significant differences according to the measurement depth(p<0.05). 99mTc-pertechnetate has a negative correlation coefficient according to the depth, and the error of the measured value was negligible at a depth from 0 cm to 7 cm at 0.3 mL and 0.5 mL, and the range of error increased as the volume increased. Conclusion In clinical practice, it is sometimes installed differently than the Standard depth recommended by the equipment company. If it's measured at the recommended depth and volume, it could be thought that unnecessary exposure of the operator and the patient will be reduced, and more accurate radiation exams will be possible in quantitative analysis.

Surface Treatment of Eggshells with Low-Energy Electron Beam

  • Kataoka, Noriaki;Kawahara, Daigo;Sekiguchi, Masayuki
    • Journal of Radiation Protection and Research
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    • v.46 no.1
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    • pp.8-13
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    • 2021
  • Background: Salmonella enteritidis (SE) was the main cause of the pandemic of foodborne salmonellosis. The surface of eggs' shells can be contaminated with this bacterium; however, washing them with sodium hypochlorite solution not only reduces their flavor but also heavily impacts the environment. An alternative to this is surface sterilization using low-energy electron beam. It is known that irradiation with 1 kGy resulted in a significant 3.9 log reduction (reduction factor of 10,000) in detectable SE on the shell. FAO/IAEA/WHO indicates irradiation of any food commodity up to an overall average dose of 10 kGy presents no toxicological hazard. On the other hand, the Food and Drug Administration has deemed a dose of up to 3 kGy is allowable for eggs. However, the maximum dose permitted to be absorbed by an edible part (i.e., internal dose) is 0.1 Gy in Japan and 0.5 Gy in European Union. Materials and Methods: The electron beam (EB) depth dose distribution in the eggshell was calculated by the Monte Carlo method. The internal dose was also estimated by Monte Carlo simulation and experimentation. Results and Discussion: The EB depth dose distribution for the eggshells indicated that acceleration voltages between 80 and 200 kV were optimal for eggshell sterilization. It was also found that acceleration voltages between 80 and 150 kV were suitable for reducing the internal dose to ≤ 0.10 Gy. Conclusion: The optimum irradiative conditions for sterilizing only eggshells with an EB were between 80 and 150 kV.

An Experimental Dosimetry of Irregularly-Shaped-Field Using Therapeutic Planning Computer (치료계획용 콤퓨터를 이용한 부정형 조사면의 선량분포에 관한 실험)

  • Park, Joo-Sun;Lee, Gui-Won;Han, Yong-Moon;Kwon, Hyoung-Cheol;Yoon, Sei-Chul
    • The Journal of Korean Society for Radiation Therapy
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    • v.2 no.1
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    • pp.87-92
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    • 1987
  • The authors have intended to measure intrinsic dose distribution by Farmer dosimeter in irregularly shaped fields such as L, M, T,-shape model in order to determine dose inhomogeneity in those models. We made 2 off-axis points in each model and measured the depth dose at 1.5,5, and 9cm below surface. The results showed $1-3\%$ dose discrepancy between 2 points. We also measured the depth dose by geometric approximation and computer calculation in those models, and came to the conclusion that computer calculation using Clarkson's principle is simpler and the measurements are to the ideal data obtained by the experiment in those three models of irregularly shaped fields than those of geometric approximation method.

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An Experimental Dosimetry of Irregularly Shaped Fields Using Therapeutic Planning Computer (치료계획용 컴퓨터를 이용한 부정형조사면의 선량분포에 관한 실험)

  • Kwon Hyoung Cheol;Oh Yoon Kyeong;Yoon Sei Chul;Bahk Young Whee
    • Radiation Oncology Journal
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    • v.2 no.2
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    • pp.281-285
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    • 1984
  • The authors have intended to measure intrinsic dose distribution by Farmer dosimeter in irregularly shaped fields such as L.M and T shape models in order to determine dose inhomogeneity in those models. We made 2 off·axis points in each model and measured the depth dose at 1.5, 5 and 9cm below surface. The results showed $l\~3\%$ dose discrepancy between 2 points. We also measured the depth dose by geometric approximation and computer calculation in those models, and came to the conclusion that computer calculation using Clarkson's principle is simpler and the measurements are closer to the ideal data obtained by the experiment in three models of irregularly shaped fields than those of geometric approximation method.

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Fast Neutron Beam Dosimetry (속중성자선의 선량분포에 관한 연구)

  • 지영훈;이동한;류성렬;권수일;신동오;박성용
    • Progress in Medical Physics
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    • v.8 no.2
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    • pp.45-57
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    • 1997
  • It is mandatory to measure accurately the dose distribution and the total absorbed dose of fast neutron for putting it to the clinical use. At present the methods of measurement of fast neutron are proposed largely by American Associations of Physicists in Medicine, European Clinical Neutron Dosimetry Group, and International Commission on Radiation Units and Measurements. The complexity of measurement, however, induces the methodological differences between them. In our study, therefore, we tried to establish a unique technique of measurement by means of measuring the emitted doses and the dose distribution of fast neutron beam from neutron therapy machine, and to invent a standard method of measurement adequate to our situation. For measuring the absorbed doses and the dose distribution of fast neutron beam, we used IC-17 and IC-18 ion chambers manufactured by A-150 plastic(tissue-equivalent material), IC-17M ion chamber manufactured by magnesium, TE gas and Ar gas, and RDM 2A electrometer. The magnitude of gamma-contamination intermingled with fast neutron beam was about 13% at 5cm depth of standard irradiated field, and increased as the depth was increased. At the central axis the maximum dose depth and 50% dose depth were 1.32cm and 14.8cm, respectively. The surface dose rate was 41.6-54.1% throughout the entire irradiated fields and increased as the irradiated fields were increased. Beam profile was that the horn effect of about 7.5% appeared at 2.5cm depth and the flattest at 10cm depth.

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A Study on the Lattic Damages and Impurity Depth Profiles of ${BF^+}_2$ Ion Implanted Silicon (${BF^+}_2$ 이온 주입된 실리콘 시료의 격자손상과 불순물 농도분포에 대한 연구)

  • 권상직;백문철;차주연;권오준
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.25 no.3
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    • pp.294-301
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    • 1988
  • A study on the lattice damages and impurity depth profiles have been performed with BF2 ion implanted silicon materials. Electrical measurement, SIMS and TEM analysis techniques were used in order to identify the reverse annealing phenomena, impurity depth profiles and lattice damages. A typical reverse annealing phenomena were shown at the dose of 1x10**15/cm\ulcorner and non-reverse annealing at the dose of 5x10**15/cm\ulcorner This was explained with the formation of the amorphous region at BF2+ ion implantation with high dose. That is, the amorphous reigons were recrystallized centrated at certain regions were measured by SIMS technique. The dislocation loops-like crystalline defects were observed with TEM cross sections, which were formed at the lattice damaged region during annealing process.

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Analysis of dose from surface to near the buildup region in the therapeutic X-ray beam (표피로 부터 buildup 영역까지 흡수되는 암치료용 방사선의 선량분석)

  • Vahc, Young-Woo
    • Progress in Medical Physics
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    • v.6 no.2
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    • pp.41-50
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    • 1995
  • The absorbed dose and contaminant electron distribution of therapeutic X-ray beam (15MV photon) was studied with a half blocked beams of 30$\times$30$\textrm{cm}^2$ and field size ranging from 5$\times$5 to 30$\times$30$\textrm{cm}^2$. For a 15MV photon beam energy, the value of the depth of dose maximum, d$_{max}$, gradually decrease with increasing field size from 5$\times$5 to 30$\times$30$\textrm{cm}^2$ due to mainly by contaminant electrons which are produced in the flattening filter and scattered by collimator jaws, tray holder〔Lucite〕, blocking block and air. The results suggest that separate dosimetry data should be kept for blocked and unblocked field. The inherence of the contaminant electrons to the open field depth of maximum dose can lead to mistaken results if attenuation measurements are made at that depth. A nurmerous contaminant electrons mainly were distributed as shape of corn in the central photon beam and their path length in the water were shorter than 30mm because of the electrons energy having around 6MeV. These results clearly appears that the substraction of scattered electrons (electrons and positrons) from the total depth dose curve not only lowers the absolute dose in the bulidup region and surface dose, it also causes a shift of d$_{max}$ to a deeper depth. In the terapeutic high energy photon beam, the absorbed dose near the buildup region is the combined result of incident contaminant electrons and phantom generated electronsrons.

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