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Article type: Cover
1994 Volume 50 Issue 9 Pages
Cover23-
Published: September 01, 1994
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Article type: Index
1994 Volume 50 Issue 9 Pages
Toc23-
Published: September 01, 1994
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Article type: Index
1994 Volume 50 Issue 9 Pages
Toc24-
Published: September 01, 1994
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Article type: Appendix
1994 Volume 50 Issue 9 Pages
i-iv
Published: September 01, 1994
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Article type: Appendix
1994 Volume 50 Issue 9 Pages
iv-ix
Published: September 01, 1994
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EISHU SHINKAI, SEISUKE EZOE, NOBORU SHIGETANI, SEIGI IRIE, TAKASHI IZU ...
Article type: Article
1994 Volume 50 Issue 9 Pages
1565-1572
Published: September 01, 1994
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It has been reported that the Japanese average medical exposure exceeds twice that of the United States and Europe. This growing awareness of excessive exposure has prompted studies to reduce patient exposure, and as a result, preventive measures are beginning to be enforced in many institutions. For this purpose we have been researching and have developed a dosimeter capable of estimating patient dose accurately. In our former report, we introduced a device called an"Area Exposure Product"meter. This time, we have developed a new"Double Electrode Ionization Chamber"and an amplifier which can measure the exposed dose and area exposure product simultaneously. In this paper, we will give an outline of this chamber and its special characteristics (the dependence of dose quality, quantity, dose rate and field-output relationship and aluminum equivalent thickness) of the dosimeter. The performance of this chamber is similar to that of IONEX chamber which was used as a reference. This chamber can be used to survey area exposure product and exposure dose in front of the collimator.
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MANABU NAKATA, YOSHINORI KOMAI, TAKASHI OKADA, SATOSHI FUKUMOTO, KAZUM ...
Article type: Article
1994 Volume 50 Issue 9 Pages
1573-1580
Published: September 01, 1994
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A digital portal imaging (DPI) system for megavoltage photon beams was installed recently in our department. The purpose of this study is to evaluate the image quality of this system. We have analyzed the following properties of the system; relationship between measured dose-rate and pixel values of the DPI, spatial resolution, detectability of low-contrast objects and setup errors. The results were compared with those of conventional screen-film systems. As a result, the relationship between the measured dose-rate and the pixel value of the DPI was found to be linear in the dose-rate range between 100 and 400cGy/min. Spatial resolution was 1.25 and 0.5mm for the DPI and the screen-film systems, respectively. The slope of the contrast-detail curves differed between the DPI and the screen-film systems. The contrast thresholds were 0.6 and 0.3% for the DPI and the screen-film systems, respectively. The detectability of a setup error of 1mm and 2mm for the DPI was lower than that by the screen-film systems, although the difference was not very significant. In conclusion, the image quality of the DPI at present time is slightly inferior to the conventional screen-film systems. However, notable advantages of the DPI system are that any positional changes in patients during irradiation can be detected very quickly, and that quantitative analysis of the setup variation can be obtained. The image quality of the DPI will be improved as the technology regarding advances. Therefore, this verification system using the DPI device, is expected to be used for clinical radiation therapy in the future.
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AKIO OGURA
Article type: Article
1994 Volume 50 Issue 9 Pages
1581-1587
Published: September 01, 1994
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The detection performance of human observers has been used widely in the evaluation of imaging systems. In observer performance experiments, the detectability is affected by various factors such as object size, viewing distance, illumination, selected observer, order of reading samples and so forth. For the viewing distance, there are two situations where firstly observers are allowed to choose a suitable viewing distance and secondly they are not allowed to do so and must use a fixed viewing distance. The purpose of this paper is to assess whether the detectability of observer performance experiments is dependent on the viewing distance. The contrast-detail (C-D) diagram described the relationship between the threshold contrast in visually detectable by a human observers and viewing distance (20-200cm) using four different radiographic systems. Our results indicated that detectability by detection performance increased when observers adopted a short viewing distance for small objects and long viewing distance for large objects. It is possible that the selected viewing distance changes the evaluation of screen/film systems. Therefore, it is better that the designer of the experiment does not institute the fixed viewing distance.
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[in Japanese], [in Japanese]
Article type: Article
1994 Volume 50 Issue 9 Pages
1588-1601
Published: September 01, 1994
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[in Japanese], [in Japanese]
Article type: Article
1994 Volume 50 Issue 9 Pages
1602-1613
Published: September 01, 1994
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[in Japanese]
Article type: Article
1994 Volume 50 Issue 9 Pages
1614-1620
Published: September 01, 1994
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[in Japanese]
Article type: Article
1994 Volume 50 Issue 9 Pages
1621-1627
Published: September 01, 1994
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[in Japanese], [in Japanese]
Article type: Article
1994 Volume 50 Issue 9 Pages
1628-1638
Published: September 01, 1994
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[in Japanese]
Article type: Article
1994 Volume 50 Issue 9 Pages
1639-1650
Published: September 01, 1994
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[in Japanese], [in Japanese], [in Japanese], [in Japanese], [in Japane ...
Article type: Article
1994 Volume 50 Issue 9 Pages
1651-1677
Published: September 01, 1994
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Article type: Appendix
1994 Volume 50 Issue 9 Pages
1678-1680
Published: September 01, 1994
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Article type: Appendix
1994 Volume 50 Issue 9 Pages
1681-1683
Published: September 01, 1994
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Article type: Appendix
1994 Volume 50 Issue 9 Pages
1684-1686
Published: September 01, 1994
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Article type: Appendix
1994 Volume 50 Issue 9 Pages
1687-1698
Published: September 01, 1994
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Article type: Appendix
1994 Volume 50 Issue 9 Pages
1699-1700
Published: September 01, 1994
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Article type: Appendix
1994 Volume 50 Issue 9 Pages
1701-
Published: September 01, 1994
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Article type: Appendix
1994 Volume 50 Issue 9 Pages
1701-
Published: September 01, 1994
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Article type: Appendix
1994 Volume 50 Issue 9 Pages
1701-
Published: September 01, 1994
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Article type: Appendix
1994 Volume 50 Issue 9 Pages
App14-
Published: September 01, 1994
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Article type: Cover
1994 Volume 50 Issue 9 Pages
Cover24-
Published: September 01, 1994
Released on J-STAGE: June 29, 2017
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