After certain amount of radiation dose were given radioactivity in the parts of the 10MV and 18MV linear accelarators (target, flattening filter and reserch window shield) and the treatment aids of a 18MV linear accelerator was measured using a Ge (Int) detector in a gamma radiation spectrometer system. Immediately after a 18MV X-ray treatment, the decay curve of a dose equivalent rate a 50cm of distance from isocenter was observed using a survey meter with a X-ray recorder. At the radiotherapy department in our hospital,8,142 fields were irradiate d in 1994 with a 18MV X-ray (total fields including 6MV and electron modes were 13,534). The exposure to one technologist around the treatment head was estimated to 9654 Sv/year or 19.3g Sv/week assuming 25 working weeks per year with a 18MV X-ray treatment. In a worst case, assuming 50 working weeks and 13,534 total fields with a 18MV X-ray, the exposure was estimated to 114.31.6v/week. This value was considered to be with in the dose limits (i. e.50mSv/year) of effective dose equivalent on ICRP publication 60.
Although various modalities such as CT, CR and MRI are now used for medical images, the conventional screen-film system still plays an important role. The photographic contrast of the screen-film system is an important factor characterizing the image quality of x-ray images and is defined by the use of a characteristic curve. A polynomial approximation is usually applied to density data in order to draw the characteristic curve. This approximation has been based only on visualized judgement. In this paper, AIC in statistics is introduced as a numerical criterion for choosing one from among a number of approximated polynomials. The polynomial approximation is carried out by the introduction of AIC, and this method is accurate and efficient.
The developing temperature dependency of Fuji Advanced Radiographic System (AD system)and Fuji medical super high resolution series (HR series) was evaluated by measuring characteristic curves, resolution properties and noise RMS. Futhermore, the possibility of reductio n of patient's radiation exposure without decrease in image quality was evaluated, because the speed of screen/film systems increases as the developing temperature going up and the granuality of the AD system is greatly improved comparing with HR series. The physical imaging properties of screen/film systems were affected by the developin g temperature. But the level of the effects on AD system was smaller than HR series. It was confirmed that the granuality of AD system was improved greatly compared to HR series. Therefore, there is a possibility in reduction of patient's radiation exposure by i ncreasing the developing temperature compared with the traditional situation.
The developing temperature dependency of Kodak Insight EF/RA Image System (IEF system)was evaluated by measuring characteristic curve, resolution properties and noise RMS. Futhermore, the possibility of the reduction of the patient's exposure without decrease in image quality was evaluated. The physical imaging properties of screen/film systems were affected by the developing tempera ture. Except the gross fog, other imaging properties of IEF system on developing temperature was small. Especially it was confirmed that the developing temperature dependency of granuality of IEF system was less than those of the other new ortho screen film systems (Konica ES-C medical x-ray film of EX system and Fuji UR -1 medical x-ray film of AD system). Therefore, there is the possibility of the reduction of the patient's exposure by using the higher developing temperature than the traditional situation after due consideration of increasing the gross fog.