[en] It is important to demonstrate clearly the hepatic arteries, parasitic arteries and small stains in conventional hepatic angiography and lipiodol accumulations after transcatheter arterial embolization with lipiodol. A diaphragmatic compensating filter (DCF) covering the diaphragmatic region was made originally. The shape of DCF for a high density part of the angiogram is similar to the shape of diaphragm, but the shape for a low density part could not be specified. The smallest tolerance of the DCF was 13.2 mm on the film. Therefore, a DCF was effective in more than 95.8% of angiograms. Only one type of DCF is possible to use in combination with side compensating filters. The clinical value of the radiographic images were remarkably improved, more then 29%, by the image analyze system, PIAS LA-500. Therefore, a DCF is indispensable in conventional hepatic angiography. (author)

[en] It is empirically said that the application of the compensating filter leads to a decrease in the exposure dose of the filter-inserted area and an increase in that of the otherwise area. Using the area-dosimeter, comparison was made of exposure doses by the application of the above filter and the otherwise filter in head simple X-P, abdominal angiography and lower extremity X-P. Using the filter for head simple X-P and Mix-Dp phantom, measurement was made of the absorbed dose at the 5 cm-depth to compare the rate of decrease in absorbed dose between the above both areas. Head simple X-P gained a decrease in area dose of 29%. The absorbed dose at the 5 cm-depth in the phantom experiment showed a decrease of over 26% at the filter-inserted area, but little increase at the otherwise area. The above results indicated the interposition of the filter between the X-ray tube and the object to lead to decreases not only in the area dose but also in the patient's exposure dose. (author)

[en] In efforts to reduce the dose of X-ray exposure in mass screenings for gastric cancer, we devised lead acrylic fitters and evaluated their effectiveness using a phantom. We found that our 6 mm, 12 mm, and 24 mm filters reduced the exposure dose by 14.30%, 14.30%, and 21.40%, respectively. The reduction of the depth dose-rate calculated by the position of the stomach was 4.95%, 7.06%, and 9.34%, respectively. There was no visually discernible difference in the density of gastric images on the X-ray films obtained with or without the filters. When we measured the size of the gastric images and the filter shadows, we found that the gastric images overlapped the filter shadows in 332 of 473 (70.2%) clinical cases. However, the filter shadows presented no diagnostic disadvantage. Based on our findings, we suggest that lead acrylic filters should be introduced into mass screenings for gastric cancer to reduce the dose of X-ray exposure. (author)

[en] The usefulness of three types of lead acrylic filter in gastric cancer screening was studied on reducing effective dose. Effective dose was estimated using the software Monte Carlo program for Windows. The results indicated that each filter contributed to a reduction in effective dose; 62.63±2.10μSv for no filter, 58.86±1.70μSv for filter A, 55.80±1.98μSv for filter B and 54.10±1.80μSv for filter C. The use of lead acrylic filter in gastric cancer screening is one of effective methods to protect examinees against radiation. (author)

[en] The purpose of this study is to build a system for effective dose display immediately after the gastric cancer X-ray screening. The regression equation of effective dose and dose area product (DAP) was introduced from the data of 500 persons including DAP and effective dose calculated using program for X-ray Monte Carlo. The effective dose was 5.39 mSv of median, 1.18 mSv of minimum, and 38.38 mSv of maximum. The regression equation was Y=0.354+0.0003772X (Y: effective dose, mSv, X: DAP, mGy cm2). Using the regression equation, the effective dose can be estimated from DAP and displayed just after the individual screening. 'Effective dose display system' was constructed to display effective dose immediately after gastric cancer X-ray screening. This system is on the way to be reformed by improving the regression equation on larger data. (author)

[en] Gafchromic films have been applied to X-ray dosimetry in diagnostic radiology. To correct nonuniformity errors in Gafchromic films, X-rays in the double-exposure technique can be replaced with ultraviolet (UV)-A rays. Intensities of the incident and transmitted UV-A rays were measured. However, it is unclear whether the chemical color change of Gafchromic films affects the UV-A transmission intensity. Gafchromic EBT3 films were suitable to be used in this study because non-UV protection layers are present on both sides of the film. The film is placed between UV-A ray light-emitting diodes and a probe of a UV meter. Gafchromic EBT3 films were irradiated by UV-A rays for up to 60 min. Data for analysis were obtained in the subsequent 60 min. Images from before and after UV-A irradiation were subtracted. When using 375 nm UV-A, the mean ± standard deviation (SD) of the pixel values in the subtracted image was remarkably high (11,194.15 ± 586.63). However, the UV-A transmissivity remained constant throughout the 60 min irradiation period. The mean ± SD UV-A transmission intensity was 184.48 ± 0.50 μm/cm². Our findings demonstrate that color density changes in Gafchromic EBT3 films do not affect their UV-A transmission. Therefore, Gafchromic films were irradiated by UV-A rays as a preexposure. (author)

[en] The purpose of this study is to develop a method for use at extremely low-dose ranges and to decrease the uncertainty outside the recommended range of Gafchromic RTQA2 (RTQA2). By this method, the CT dose including the scattered radiation region can be grasped. The base density was increased by ultraviolet (UV)-ray preirradiation. RTQA2 was irradiated with UV-A rays for 26 and 40 h. Subsequently, RTQA2 was exposed to 2, 4, 6, 8, 10, 25, 50, 75, 100, 150, 200 and 250 mGy X-rays using a segmentation method. Calibration curves with and without UV-A irradiation were compared. The calibration curve with 40-h UV-A ray irradiation was the most linear, and a steeper slope area was not observed. The uncertainty in the calibration curve was reduced (p < 0.05). UV-A ray irradiation is an effective method for treating RTQA2; the accuracy in the extremely low-dose range of RTQA2 was improved. (authors)

[en] Recently developed radiochromic films can easily be used to measure absorbed doses because they do not need development processing and indicate a density change that depends on the absorbed dose. However, in GAFCHROMIC EBT2 dosimetry (GAF-EBT2) as a radiochromic film, the precision of the measurement was compromised, because of non-uniformity problems caused by image acquisition using a flat-bed scanner with a transmission mode. The purpose of this study was to improve the precision of the measurement using a flat-bed scanner with a reflection mode at the low absorbed dose dynamic range of GAF-EBT2. The calibration curves of the absorbed dose versus the film density for GAF-EBT2 were provided. X-rays were exposed in the range between ~0 and 120 mGy in increments of about 12 mGy. The results of the method using a flat-bed scanner with the transmission mode were compared with those of the method using the same scanner with the reflection mode. The results should that the determination coefficients (r²) for the straight-line approximation of the calibration curve using the reflection mode were higher than 0.99, and the gradient using the reflection mode was about twice that of the one using the transmission mode. The non-uniformity error that is produced by a flat-bed scanner with the transmission mode setting could be almost eliminated by converting from the transmission mode to the reflection mode. In light of these findings, the method using a flat-bed scanner with the reflection mode (only using uniform white paper) improved the precision of the measurement for the low absorbed dose range.

[en] In this paper, we propose a novel radiochromic film (RCF)-based computed tomography (CT) dosimetry method, which is different from the method based on CT dose index. RCF dosimetry using Gafchromic QA2 films was performed using two lengths of film-folding phantoms. The phantom was exposed to X-ray CT through a single scan, while the RCF was sandwiched between the phantoms. We analysed the dose profile curve in two directions to investigate the dose distribution. We observed a difference in the dose distribution as the phantom size changed. Our results contradict with the results of previous studies such as Monte Carlo simulation or direct measurement. The ability to visually evaluate 2D dose distributions is an advantage of RCF dosimetry over other methods. This research investigated the ability of 2D X-ray CT dose evaluation using RCF and film-folding phantom. (authors)