The purpose of this study is to develop a numerical model for compressed breast of Japanese women which can evaluate the radiation dose in mammography. The model should take account of the average data for thickness of the compressed breast, and area, height and width of the mammograms. The compressed breast thickness is typically 4.4 to 6.4cm for European and American women, whereas it is under 3.8cm for Japanese women. Therefore, applying the European and American models without any modification for Japanese women would result in an overestimation of the absorbed dose. The data of 560 mammograms were analyzed focusing on the size and geometry of the projected images (cranio-caudal) to formulate a compressed breast phantom. An extremely good linear coefficient of correlation (0.98) between the area and the product of the width and height of the projected images was found. A numerical model describing a part of a simple elliptic column was constructed from this relationship and the averaged thickness (3.15cm) of the compressed breast. This model will lead to a realistic estimation of the total volumetric absorbed dose in mammography.

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Recently a high-performance PET scanner, which measures depth-of-interaction (DOI) information, is being developed for molecular imaging. DOI measurement of multi-layered thin crystals can improve spatial resolution and scanner sensitivity simultaneously. In this paper, we apply an algebraic image reconstruction method to 2-dimensional (2D) DOI-PET scanners using accurate system modeling, in order to evaluate the effects of using DOI information on PET image quality. Algebraic image reconstruction methods have been successfully used to improve PET image quality, compared with the conventional filtered backprojection method. The proposed method is applied to simulated data for a small 2D DOI-PET scanner. The results show that accurate system modeling improves spatial resolution without noise emphasis, and that DOI information improves uniformity of spatial resolution.

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The development of computerized tomography (CT) has made CT fluoroscopy possible with real-time CT images. However examination are expected to have high medical and occupational exposures. Then, exposures to patients and operating and assisting physicians during the CT fluoroscopy-guided lung biopsy were estimated. And changes in the examination conditions to lower the dose were made.
Patient exposure was measured using an anthropomorphic pha ntom by simulation of clinical examination conditions. The surface dose to the physician was measured during actual clinical examinations. The average effective dose for the patient was 34 ±22mSv. The highest surface dose amounted to 1.9 Gy, although this was in a very narrow field. Patient doses could be reduced by a factor of 2.5-3 by changing examination methods while still retaining 'diagnostic quality. The highest dose to the operating physician was lOmGy which was recorded on the back of the hand and the average effective dose was estimated as 5.99μSv per 1-minute examination. Doses were reduced by about a factor of 50 by lowering the tube voltage from 120kV to 80 kV and using a supplementary tool. The doses for assisting physicians were not significant.
The exposure for physicians and patients was much affected b y lowering the tube voltage used for fluoroscopy. Using a supplementary tool was effective for reducing the dose for physicians.

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It is important to position patient accurately in radiation therapy which has a good dose concentration especially, in charged particle radiotherapy. Misalignment of patient to the center of the beam axis causes complication of normal tissue and low dose in the target volume due to the concentration. Hyogo Ion Medical Center has a patient positioning system which can position within lmm. The system consists of X-ray TV system to detect displacement of patient and treatment couch which have 6 axes (3 translations and 3 rotations) to move patient accurately. Since the couch has 3 rotation axes, it is very difficult to express the displacement with translations and rotations of patient by the couch movements. Therefore, expression of translation and rotation to compensate the patient displacement was derived. Test of the expression was done in the patient positioning system. X-ray images were taken before and after moving the couch, and the actual displacement and the calculated one for 6axis were compared. The actual and the calculated agreed each other within lmm for translation and 0.1 deg for rotation.

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