• Title, Summary, Keyword: Water phantom

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The Comparison of Absolute Dose due to Differences of Measurement Condition and Calibration Protocols for Photon Beams (6MV 광자선에서 측정조건의 변화와 측정법의 차이에 의한 절대 선량값의 비교)

  • Kim, Hoi-Nam
    • The Journal of Korean Society for Radiation Therapy
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    • v.10 no.1
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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.

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Application of IAEA TRS-398 Protocol to Gamma Knife Model C (감마나이프 C모델에 대한 IAEA TRS-398 프로토콜의 적용)

  • Chung, Hyun-Tai
    • Progress in Medical Physics
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    • v.18 no.4
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    • pp.194-201
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    • 2007
  • Although Gamma Knife irradiates much more radiation in a single session than conventional radiotherapy, there were only a few studies to measure absolute dose of a Gamma Knife. Especially, there is no report of application of International Atomic Energy Agency (IAEA) TRS-398 which requires to use a water phantom in radiation measurement to Gamma Knife. In this article, the authors reported results of the experiments to measure the absorbed dose to water of a Gamma Knife Model C using the IAEA TRS-398 protocol. The absorbed dose to water of a Gamma Knife model C was measured using a water phantom under conditions as close as possible to the IAEA TRS-398 protocol. The obtained results were compared with values measured using the plastic phantom provided by the Gamma Knife manufacturer. Two Capintec PR-05P mini-chambers and a PTW UNIDOS electrometer were used in measurements. The absorbed dose to water of a Gamma Knife model C inside the water phantom was 1.38% larger than that of the plastic phantom. The current protocol provided by the manufacturer has an intrinsic error stems from the fact that a plastic phantom is used instead of a water phantom. In conclusion, it is not possible to fully apply IAEA TRS-398 to measurement of absorbed dose of a Gamma Knife. Instead, it can be a practical choice to build a new protocol for Gamma Knife or to provide a conversion factor from a water phantom to the plastic phantom. The conversion factor can be obtained in one or two standard laboratories.

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Conversion Factors for Calibration of Personnel Dosimeters (개인선량계 교정을 위한 환산인자 계산)

  • Lee, Won-Koo;Lee, Tae-Young;Ha, Chung-Woo
    • Journal of Radiation Protection and Research
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    • v.16 no.1
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    • pp.25-32
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    • 1991
  • MCNP code was used to calculate conversion factor H(d)ma at the depths of 0.07 and 10mm within a water phantom recommended by IAEA and within a PMMA phantom required by the US dosimeter proficiency testing programmes. The calculations were performed for an expanded parrallel beam of monoenergetic photons of perpendicular incidence on one faces of the phantom. The results can be used as conversion factor in calibrating individual dosemeters in terms of the dose equivalent quantities defined directly in the phantom.

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Evaluation of Planning Dose Accuracy in Case of Radiation Treatment on Inhomogeneous Organ Structure (불균질부 방사선치료 시 계획 선량의 정확성 평가)

  • Kim, Chan Yong;Lee, Jae Hee;Kwak, Yong Kook;Ha, Min Yong
    • The Journal of Korean Society for Radiation Therapy
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    • v.25 no.2
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    • pp.137-143
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    • 2013
  • Purpose: We are to find out the difference of calculated dose of treatment planning system (TPS) and measured dose in case of inhomogeneous organ structure. Materials and Methods: Inhomogeneous phantom is made with solid water phantom and cork plate. CT image of inhomogeneous phantom is acquired. Treatment plan is made with TPS (Pinnacle3 9.2. Royal Philips Electronics, Netherlands) and calculated dose of point of interest is acquired. Treatment plan was delivered in the inhomogeneous phantom by ARTISTE (Siemens AG, Germany) measured dose of each point of interest is obtained with Gafchromic EBT2 film (International Specialty Products, US) in the gap between solid water phantom or cork plate. To simulate lung cancer radiation treatment, artificial tumor target of paraffin is inserted in the cork volume of inhomogeneous phantom. Calculated dose and measured dose are acquired as above. Results: In case of inhomogeneous phantom experiment, dose difference of calculated dose and measured dose is about -8.5% at solid water phantom-cork gap and about -7% lower in measured dose at cork-solid water phantom gap. In case of inhomogeneous phantom inserted paraffin target experiment, dose difference is about 5% lower in measured dose at cork-paraffin gap. There is no significant difference at same material gap in both experiments. Conclusion: Radiation dose at the gap between two organs with different electron density is significantly lower than calculated dose with TPS. Therefore, we must be aware of dose calculation error in TPS and great care is suggested in case of radiation treatment planning on inhomogeneous organ structure.

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Utility Evaluation of Supportive Devices for Interventional Lower Extremity Angiography (인터벤션 하지 혈관조영검사를 위한 보조기구의 유용성 평가)

  • Kong, Chang gi;Song, Jong Nam;Jeong, Moon Taek;Han, Jae Bok
    • Journal of the Korean Society of Radiology
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    • v.13 no.4
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    • pp.613-621
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    • 2019
  • The purpose of this study is to evaluate the effectiveness of supportive devices which are for minimizing the patient's movement during lower extremity angiography and to verify image quality of phantom by analyzing of Mask image, DSA image and Roadmap image into SNR and CNR. As a result of comparing SNR with CNR of mask image obtained by DSA technique using the phantom alone and phantom placed on the supportive devices, there was no significant difference between about 0~0.06 for SNR and about 0~0.003 for CNR. The study showed about 0.11~0.35 for SNR and 0.016~0.031 for CNR of DSA imaging by DSA technique about only water phantom of the blood vessel model and the water phantom placed on the device. Analyzing SNR and CNR of Roadmap technique about water phantom on the auxiliary device (hardboard paper, pomax, polycarbonate, acrylic) and water phantom alone, there was no significant difference between 0.02~0.05 for SNR and 0.002~0.004 for CNR. In conclusion, there was no significant difference on image quality by using supportive devices made by hardboard paper, pomax, polycarbonate or acryl regardless of whether using supportive devices or not. Supportive devices to minimize of the patient's movement may reduce the total amount of contrast, exam-time, radiation exposure and eliminate risk factors during angiogram. Supportive devices made by hardboard paper can be applied easily during angiogram due to advantages of reasonable price and simple processing. It is considered that will be useful to consider cost efficiency and types of materials and their properties in accordance with purpose and method of the study when the operator makes and uses supportive devices.

A Study on the absorbed dose to water for high energy electron beams using Water equivalency of plastic phantom (고 에너지 전자선에서 물등가 고체팬톰을 이용한 물 흡수선량 측정에 관한 연구)

  • Sin, Dong-Ho;Sin, Dong-Oh;Kim, Sung-Hoon;Park, Sung-Yong;Ji, Young-Hoon;Ahn, Hee-Kyung;Kang, Jin-Oh;Hong, Seong-Eon
    • Proceedings of the Korean Society of Medical Physics Conference
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    • pp.166-169
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    • 2004
  • In the International Code of Practice for dosimetry TRS-398 published by International Atomic Energy Agency(IAEA), water equivalency plastic phantom may be used under certain circumstances for electron beam dosimetry for beam quality E0${\leq}$ 10 MeV. In this study, Palstic Water$^{TM}$ and Virtual Water$^{TM}$ were evaluated in order to determine fluence scaling factor hpl. Plastic phantom was evaluated for five electron energy from 6 MeV to 20 MeV. From the measured data of Palstic Water$^{TM}$, the fluence scaling factor hpl was found to be average 0.9964 and Virtual Water$^{TM}$ fluence scaling factor was 1.0156.

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Properties of Water Substitute Solid Phantoms for Electron Dosimetry

  • Saitoh, Hidetoshi;Tomaru, Teizo;Fujisaki, Tatsuya;Abe, Shinji;Myojoyama, Atsushi;Fukuda, Kenichi
    • Proceedings of the Korean Society of Medical Physics Conference
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    • pp.255-259
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    • 2002
  • To reduce the uncertainty in the calibration of radiation beams, absorbed dose to water for high energy electrons is recommended as the standards and reference absorbed dose by AAPM Report no.51 and IAEA Technical Reports no.398. In these recommendations, water is, defined as the reference medium, however, the water substitute solid phantoms are discouraged. Nevertheless, when accurate chamber positioning in water is not possible, or when no waterproof chamber is available, their use is permitted at beam qualities R$\_$50/ < 4 g/cm$^2$ (E$\_$0/ < 10 MeV). For the electron dosimetry using solid phantom, a depth-scaling factor is used for the conversion of depth in solid phantoms to depth in water, and a fluence-scaling factor is used for the conversion of ionization chamber reading in plastic phantom to reading in water. In this work, the properties, especially depth-scaling factors c$\_$p1/ and fluence-scaling factors h$\_$pl/ of several commercially available water substitute solid phantoms were determined, and the electron dosimetry using these scaling method was evaluated. As a result, it is obviously that dose-distribution in solid phantom can be converted to appropriate dose-distribution in water by means of IAEA depth-scaling.

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Development of a Pelvic Phantom for Dose Verification in High Dose Rate (HDR) Brachytherapy

  • Jang, Ji-Na;Suh, Tae-Suk;Huh, Soon-Nyung;Kim, Hoi-Nam;Yoon, Sei-Chul;Lee, Hyoung-Koo;Choe, Bo-Young
    • Proceedings of the Korean Society of Medical Physics Conference
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    • pp.150-153
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    • 2002
  • High dose rate (HDR) brachytherapy in the treatment of cervix carcinoma has become popular, because it eliminated many of the problems with conventional brachytherapy. In order to improve clinical effectiveness with HDR brachytherapy, dose calculation algorithm, optimization procedures, and image registrations should be verified by comparing the dose distributions from a planning computer and those from a humanoid phantom irradiated. Therefore, the humanoid phantom should be designed such that the dose distributions could be quantitatively evaluated by utilizing the dosimeters with high spatial resolution. Therefore, the small size of thermoluminescent dosimeter (TLD) chips with the dimension of 1/8" and film dosimetry with spatial resolution of <1mm used to measure the radiation dosages in the phantom. The humanoid phantom called a pelvic phantom is made of water and tissue-equivalent acrylic plates. In order to firmly hold the HDR applicators in the water phantom, the applicators are inserted into the grooves of the applicator supporters. The dose distributions around the applicators, such as Point A and B, can be measured by placing a series of TLD chips (TLD-to- TLD distance: 5mm) in three TLD holders, and placing three verification films in orthogonal planes.

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Evaluation of Roadmap Image Quality by Parameter Change in Angiography (혈관조영검사에서 매개변수 변화에 따른 Roadmap 영상의 화질평가)

  • Kong, Chang gi;Song, Jong Nam;Han, Jae Bok
    • Journal of the Korean Society of Radiology
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    • v.14 no.1
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    • pp.53-60
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    • 2020
  • The purpose of this study is to identify factors affecting picture quality in Roadmap images, which were studied by varying the dilution rate, collimation field and flow rate of contrast medium. For a quantitative evaluation of the quality of the picture, a 3mm vessel model Water Phantom was self-produced using acrylic, a roadmap image was acquired with a self-produced vascular model Water Phantom, and the SNR(Signal to Noise Ratio) and CNR (Contrast to Noise Ratio) were analyzed. CM:N/S In the study on the change of dilution rate, CM:N/S dilution rate changed to (100%~10%:100%), and the measurement of the roadmap image taken using the vascular model Water Phantom showed that the measurement value of SNR gradually decreased as the N/S dilution rate was increased, and the measurement of CNR was gradually reduced. It was confirmed that the higher the dilution rate of CM:N/S, the lower the SNR and CNR, and also significant image can be obtained at the dilution rate of CM:N/S (100%~70:30%). The study showed the value of SNR and CNR in Roadmap image was increased as the Collimation Field was narrowed to the center of the vascular phantom; the Collimation Field was narrowed to the center of the vessel model by 2cm intervals to 0cm through 12cm. To verify the relationship with Roadmap image and Flow Rate, volume of the autoinjector was kept constant at 15 and the flow rate was gradually increased 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. The value of SNR and CNR of images taken by using water Phantom gradually decreased as the Flow Rate increased, but at Flow Rate 9 and 10, the SNR and CNR value was increase. It was not possible to confirm the relationship with SNR and CNR by ROI mean value and Background mean value. It is considered that further study is needed to evaluate the correlation about Roadmap image and Flow Rate. In conclusion, as the dilution rate of N/S in contrast medium was increased, the value of SNR and CNR was decreased. The narrower the Collimation Field, the higher image quality by increasing value of SNR and CNR. However, it is not confirmed the relationship Roadmap image and Flow Rate. It is considered that appropriate contrast medium concentration to minimize the effects of kidney and proper Collimation Field to improve contrast of image and reduce exposure X-ray during procedure is needed.

Estimation of Computed Tomography Dose in Various Phantom Shapes and Compositions (다양한 팬텀 모양 및 재질에 따른 전산화단층촬영장치 선량 평가)

  • Lee, Chang-Lae
    • Journal of radiological science and technology
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    • v.40 no.1
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    • pp.13-18
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    • 2017
  • The purpose of this study was to investigate CTDI (computed tomography dose index at center) for various phantom shapes, sizes, and compositions by using GATE (geant4 application for tomographic emission) simulations. GATE simulations were performed for various phantom shapes (cylinder, elliptical, and hexagonal prism PMMA phantoms) and phantom compositions (water, PMMA, polyethylene, polyoxymethylene) with various diameters (1-50 cm) at various kVp and mAs levels. The $CTDI_{100center}$ values of cylinder, elliptical, and hexagonal prism phantom at 120 kVp, 200 mAs resulted in 11.1, 13.4, and 12.2 mGy, respectively. The volume is the same, but $CTDI_{100center}$ values are different depending on the type of phantom. The water, PMMA, and polyoxymethylene phantom $CTDI_{100center}$ values were relatively low as the material density increased. However, in the case of Polyethylene, the $CTDI_{100center}$ value was higher than that of PMMA at diameters exceeding 15 cm ($CTDI_{100center}$ : 35.0 mGy). And a diameter greater than 30 cm ($CTDI_{100center}$ : 17.7 mGy) showed more $CTDI_{100center}$ than Water. We have used limited phantoms to evaluate CT doses. In this study, $CTDI_{100center}$ values were estimated and simulated by GATE simulation according to the material and shape of the phantom. CT dosimetry can be estimated more accurately by using various materials and phantom shapes close to human body.