Japanese Journal of Medical Physics (Igakubutsuri)
Online ISSN : 2186-9634
Print ISSN : 1345-5354
ISSN-L : 1345-5354
Volume 22, Issue 2
Displaying 1-9 of 9 articles from this issue
  • A guidance level and the present situation of mammographic dose
    Hiroshi Terada
    2002 Volume 22 Issue 2 Pages 65-73
    Published: June 30, 2002
    Released on J-STAGE: September 24, 2012
    JOURNAL FREE ACCESS
    Mammography practiced for the detection of breast carcinomas requires an appropriate X ray equipment which can meet the performance standard. Also it is necessary to meet the requirements for the exposure dose as well as image quality.
    Factors affecting the exposure dose are X ray equipment, especially target-filter combination, recording systems, compression of breast, structural characteristics of breast and etc. The current guidance for the mammography adopts 3mGy as a dose level for standard breast for a direction which is recommended by IAEA. However, the average glandular dose for the mammography was 1.5mGy according to the image evaluation survey of medical institution as of December,2001. This figure is almost equal to the result given by the national survey conducted from 1997 to 1998.
    The exposure reduction depends on the technique of radiological technologists. It is needed for them to optimize affecting factors. When reducing breast thickness by at least 1cm, the exposure does can be reduced by 50%.
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  • Consideration about Radiation from the Point of a radiologist's View
    Eriko Tohno
    2002 Volume 22 Issue 2 Pages 74-80
    Published: June 30, 2002
    Released on J-STAGE: September 24, 2012
    JOURNAL FREE ACCESS
    Mammography is becoming popular rapidly in Japan because it is now admitted as a modality for breast screening. Radiation will not cause any adverse effect if mammography screening is done for women over 50 years old, every other year and by only MLO (medio-lateral oblique) view as this is recommended by the government. Radiation for one view is regulated to be less than 3mGy. Radiation by mammography may become problem if it is done for younger women, by more views (i. e. cranio-caudal, other additional views) and more often especially for follow up. Radiation may be more if the system is not adequate. In Japan mammograms are read by surgeons in many institutions and there are not enough medical physicists in each hospital. Cooperation between medical physicists, radiographers and radiologists will be necessary to achieve good quality mammography with adequate radiation.
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  • Hiroshi Takagi
    2002 Volume 22 Issue 2 Pages 81-87
    Published: June 30, 2002
    Released on J-STAGE: September 24, 2012
    JOURNAL FREE ACCESS
    Shortening scan time of CT scanner system has been evolved and increase in number of CT examinations has also been remarkable. This has been resulted from global recognition of usefulness of the CT examination, contrary to this merit, however, it is important to recognize the risk of x-ray exposure dose. Japan Industry Association of Radiological Systems (JIRA) in which CT manufacturers join has issued the concrete countermeasure and guidance for reduction in x-ray exposure dose in response to the ICRP90 Recommendation.
    Current CT scanner systems provide the data related to x-ray exposure dose such as CTDIW for setting CT scan parameters. To reduce x-ray exposure dose against infant patient, the scan parameters specified to infant patient (CT infant protocol) can be provided.
    Exposure dose by x-ray CT can be measured by the measurement method corresponding to IEC-60601-2-44 and by using phantom. CTDI measurement is made by CTDI100 that measures in a range of 100mm for all slice thicknesses, and absorbed radiation dose is converted to that of air.
    Dose profile is measured by using multiple thermoluminescence dosimeter (TDL) chips. CT exposure dose data including CTDI100 and Dose profile are well-defined, and Dose Information Guide conforming to IEC-60601-2-44 is provided to user for the purpose of reducing x-ray exposure dose.
    Studies by low dose (2.5 3mA) simulation for the purpose of reducing x-ray exposure dose in screening CT examination of lung cancer and development of ROI scan to reduce x-ray exposure dose in puncture under CT fluoroscopy have also been conducted.
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  • A recommendation of dosimetry by film method
    Motokatsu Yasutomo, Hirofumi Yagi
    2002 Volume 22 Issue 2 Pages 88-97
    Published: June 30, 2002
    Released on J-STAGE: September 24, 2012
    JOURNAL FREE ACCESS
    Already, the 30 years have passed since that the CT scanner was developed by Hunsfield. And now above 16,000 sets are at work.
    On the other hand, as the improvem ents of image reconstruction algorithm and variations of scan method, the medical exposure is increasing. For example, in the case of computed radiography, medical exposure is stability by using an auto exposure controller but in the case of CT, there is no unit and usually the exposure condition of CT examination are used that of recommended an exposurecondition by maker. So the medical exposure greatly differs according to the operators or the kinds of CT scanner.
    In addition, there is the close connection betwe en the x-ray intensity and the image quality. Especially, in the case of CT scanner there is no saturation of x-ray intensity like the optical density of film screen system because the digital radiographic systems have the wide dynamic range. So the increase in x-ray intensity makes a contribution to improvement of the image quality. But the increase in x-ray intensity makes axcontribution to the increase in medical exposure.
    Therefore it is very important that the CT operators grasp the medical exposure per each CT examination and patient.
    There are many met hods of medical exposure dosimetry on CT examination. But almost all the methods except the film method are impossible to get the medical exposure per each CT examination and patient.
    So in this paper the film method is recommended. Because the film method is low-priced, simple, easy and immediately shows the medical exposure per each CT examination and patient.
    Furthermore, it is confirmed that the film method is getting the correct medical exposure because that values gotten by the film method and ionization chamber are almost equivalent.
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  • Junji Tanaka
    2002 Volume 22 Issue 2 Pages 98-104
    Published: June 30, 2002
    Released on J-STAGE: September 24, 2012
    JOURNAL FREE ACCESS
    Radiologically guided interventional procedures may result in excessive radiation dose for the patients. During the last decade, more than 70 cases of radiation skin injuries have been reported. This may be partly because the potential dangers of X-radiation are not yet well recognized by the physicians, and also by lacking of practical and reliable way to monitor the dose of X-ray radiation at the radiology suite. The author presents a few recommendable techniques to monitor the patient's radiation doses during interventional radiological procedures, which may be helpful in preventing patient's radiation injury.
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  • Takaji Saito
    2002 Volume 22 Issue 2 Pages 105-109
    Published: June 30, 2002
    Released on J-STAGE: September 24, 2012
    JOURNAL FREE ACCESS
    “The radiation protection measures from equipment side, from a maker's point of view.”TAKAJI SAITO Medical Solutions Marketing Division, Siemens Asahi Medical Technologies Ltd.
    Takin g care of limited fluoro and acquisition time during every case is an important prerequisite for dose reduction. Latest technology provides us with a number of means for dose savings regarding patients and staff.
    Here, the practical techniques of the radiation control function in angiography system are addressed.
    •Last Image Hold (LIH)
    •Collimation without radiation on LIH
    •Pulsed fluoroscopy at high and low rates
    •Additional spectral filters in the X-ray beam
    •Display of applied dose during the procedure
    These technological measures will d efinitely contribute for dose reduction for interventional procedures.
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  • Masao Matsumoto
    2002 Volume 22 Issue 2 Pages 110-117
    Published: June 30, 2002
    Released on J-STAGE: September 24, 2012
    JOURNAL FREE ACCESS
    Several recent studies have a questionnaire survey of many hospitals regarding the radiation exposure conditions of X-ray examinations. From the survey result the entrance surface doses (first quartile, median, third quartile and mean values) have calculated by using the Numerical Dose Determination (NDD) method. The calculated result for all types of examinations showed that the median values were lower than the mean values, whereas the median values were higher than the mean values in the results reported in British NRPB 21. The median values of the results were lower than those in the NRPB 21 in England. The mean values were lower than IAEA guidance levels. The results have indicated that the medical exposure dose (entrance surface dose) is lower with Computed Radiography (CR) than with the Screen/Film (S/F) system except the case of chest radiography. In the case of chest radiography (adult patients) by CR exposure set ? up using a lower voltage and high mAs than the S/F method, the entrance surface doses were 150% of the median value for the overall examination and 160% of the median value for orthochromatic S/F systems. A difference in patient dose among hospitals using CR system was also found. Mean entrance surface dose in CR system was 0.12 mGy in a quartile,0.19 mGy in the middle and 0.27 mGy in the third quartile.
    Among the hospitals that showed higher doses of third quartile than above mentioned, dose differences of a quartile were distributed 2 to 10 times higher than mean exposure doses. Mori et al. propose guidance levels are lower than IAEA guidance levels of entrance surface doses for examinations carried out in Japanese institutions as the 3rd quartile of the dose distributions. Therefore the quality control of tube voltage, tube current and mAs and a regular measurement of exposure for X-ray units are required.
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  • Mitsuhiko Homma, Katsuyoshi Tabushi, Yasunori Obata, Tadashi Tamiya, S ...
    2002 Volume 22 Issue 2 Pages 118-124
    Published: June 30, 2002
    Released on J-STAGE: September 24, 2012
    JOURNAL FREE ACCESS
    Knowing the dose distribution in a tissue is as important as being able to measure exposure or absorbed dose in radiotherapy. Therefore, we have developed a measurement method for the dose distribution (CR dosimetry) in the phantom based on the imaging plate (IP) of the computed radiography (CR). The IP was applied for the dose measurement as a dosimeter instead of the film used for film dosimetry. The data from the irradiated IP were processed by a personal computer with 10 bits and were depicted as absorbed dose distributions in the phantom. The image of the dose distribution was obtained from the CR system using the DICOM form. The CR dosimetry is an application of CR system currently employed in medical examinations to dosimetry in radiotherapy. A dose distribution can be easily shown by the Dose Distribution Depiction System we developed this time. Moreover, the measurement method is simpler and a result is obtained more quickly compared with film dosimetry.
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  • Hajime Harauchi, Takashi Kondo, Yu Kumasaki, Masatoshi Ishibashi, Hoda ...
    2002 Volume 22 Issue 2 Pages 125-133
    Published: June 30, 2002
    Released on J-STAGE: September 24, 2012
    JOURNAL FREE ACCESS
    A multi-institutional Radiation Oncology Greater Area Database (ROGAD) was started in 1991 under the direction of the Japanese Society for Therapeutic Radiology and Oncology (JASTRO). Use of ROGAD was intended to allow reflection of results of data analysis into treatment strategy and treatment planning for individual cases, to provide quality assurance, to maximize the efficacy of radiotherapy, to allow assessment of new technologies or new modalities, and to optimize medical decision making. ROGAD collected 13,448 radiotherapy treatment cases from 325 facilities during the period from 1992 to 2001. In 2000, questionnaires were sent to 725 radiotherapy facilities throughout Japan, to further obtain the situation of the radiation oncology database. Workers at 179 facilities replied that “the protocol of my facility is different from ROGAD protocol and I must send data according to the ROGAD protocol”. So, we developed the Virtual Private Database System (VPDS) which is operated as if an oncologist had a database solely owned by his own facility, in spite of actually operating ROGAD. VPDS realizes integration of different plural databases, regardless of differences in entry methods, protocols, definitions and interpretations of contents of clinical data elements between facilities.
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