When using high energy X-rays, the dose increases at the skin surface and build-up region of beam contamination of secondary electrons coming out from the inner suface of the lineac head. At our radiotherapy department, many cases of external otitis from severe skin reactions, particularly resulting from whole brain irradiation of primary and metastatic brain tumors with a 6MV X-ray lineac, have been encountered. An investigation was made of the physical aspects of a 6 MV X-ray lineac, have been encountered. An investigation was made of the physical aspects of a 6 MV X-ray bean using three electron filters, lead lucite, lead glass and lucite to remove secondary electrons. Transparent materials for filters should be preferable for locating the light field. The following results were obtained : 1) For removing secondary electrons, a lead lucite filter was found best. 2) The lead lucite filter proved most effective for removing secondary electrons from the area of treatment. It reduced the dose of irradiation to the skin surface and build-up region, and furthermore improved the depth dose relative to that without filters. 3) From a clinical standpoint, skin reactions such as external otitis remarkably decreased using a lead lucite filter. 4) It thus appears necessary to use a high energy X-ray with newly designed filters to reduce beam contamination of secondary electrons.

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Two new bootstrap methods for determining characteristic curves of radiographic screen/film systems are presented : filter bootstrap sensitometry and modified stepwedge bootstrap sensitometry. Both are intensity-scale sensitometries since the radiaton intensity can be varied through use of a combination of inverse square and metal filters. Characteristic curves obtained by these methods are compared with those from screen/film systems using inverse square sensitometry as a reference standard of accuracy. The precision of all three methods is better than ±2% with agreement among generally being within 3% over the useful density range. By these bootstrap methods, it is possible to obtain characteristic curves agreeing well with those using the inverse square method for a relatively short distance, and make radiographic sensitometry practical and convenient at most medical institutions.

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The physical characteristics of ultra-high-speed screen-film systems (UHSS) (i. e. Quanta III (Q III), G8, G12, and KU systems) were studied and the UHSS systems were used in clinical radiography, such as infantile hip joint, fetus (pelvimetry) and urological radiography. When using a thin object and low tube voltage, the relative speeds of the UHSS systems were 2-3.5 times faster than that of a medium speed system, such as Hiscreen-A. On using a thick object and high tube voltage the relative speeds of the UHSS systems were 5-10 times faster than that of the His-A system. The G12 and KU systems showed particularly high speeds. Modulation transfer factors of the Q III and G8 systems were better than that of the other UHSS system. The sharpness of radiographic systems is important in infantile hip joint radiography, and thus the Q III, G8, and KU systems are most suitable for such a case. Because ultra-high-speed is required in fetrography, G12 and KU systems should be most suitable. Urinary organs are constructed from low spatial frequency. The image quality of the G8 system were found to be best for urological radiography.

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Recently, the value of MRI has come to be recognized and its scope of application is broadening. It is used to examine the brain. The horizontal axial view to obtain a brain image is taken most frequently, so as to visualize its anatomy and make the comparison of X-ray CT images and MRI. We thus attemptted to advice away of taking images with OML take would allow reproducibility. We studied the relation between the nose root and OML by a cephalogram. And found the former to be probuged according to the latter regardles of age the nose is on the prolongation of OML without considering ages. OML from a patient was thus make to accord with a localizer and found to be situation in the center of a magnetic field. A median view was then taken to ditermine the location of what and the angle of the image by the line through the root of the nose to the cross point of the grid. In this possible to obtain images parallel to OML at any neck position with satisfactory reproducibility.

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